More test coverage added for the optimizer trace.

Followup: update test results

Change the defaults:

-histogram_size=0
+histogram_size=254

-histogram_type=SINGLE_PREC_HB
+histogram_type=DOUBLE_PREC_HB

Adjust the testcases:
- Some have ignorable changes in EXPLAIN outputs and
  more counter increments due to EITS table reads.
- Testcases that meaningfully depend on the old defaults
  are changed to use the old values.

The Create_field::charset can contain garbage for columns
that the SQL layer does not consider as being string columns.
InnoDB considers BIT a string column for historical reasons
(and backward compatibility with old persistent InnoDB metadata),
and therefore it checked the charset.

The Field::charset() consistently is my_charset_bin for BIT,
so we can trust that one.

Fix clang warning: 'this' pointer cannot be null in well-defined C++ code;
pointer may be assumed to always convert to true

The only caller of TABLE::best_range_rowid_filter_for_partial_join()
already seems to be assuming that s->table != NULL.

When node is JOINER and bin-log is enabled but bin-log-index is not set in configuration, we use NULL pointer which causes segfault. 
Fixed by checking for NULL pointer before using variable.

Calls to wsrep_after_statement() were missing on PS protocol
codepath. Added calls after mysqld_stmt_execute() and
mysqld_stmt_bulk_execute().

Galera versions below 4.x do not generate unique sequence number
for view events. Take this into account when writing the SE checkpoint
to avoid debug assertion in InnoDB.

* Created new binlog-header file
* Fixed warning on SELECT INTO DUMPFILE
* Re-recorded the test result

Field_str::is_equal(): Do not allow instant conversions between
BIT (which is stored big-endian) and integer types (which can
be stored big-endian or little-endian, depending on storage engine).

row_sel_field_store_in_mysql_format_func(): Properly extend
narrower integer and DATA_FIXBINARY values to the current format.
DATA_FIXBINARY was incorrectly padded with 0x20 instead of 0.

In tests that directly write InnoDB data file pages,
compute the innodb_checksum_algorithm=crc32 checksums,
instead of writing the 0xdeadbeef value used by
innodb_checksum_algorithm=none. In this way, these tests
will not cause failures when executing
./mtr --mysqld=--loose-innodb-checksum-algorithm=strict_crc32

1. Renaming Type_handler_json to Type_handler_json_longtext
   There will be other JSON handlers soon, e.g. Type_handler_json_varchar.

2. Making the code more symmetric for data types:

- Adding a new virtual method
  Type_handler::Column_definition_validate_check_constraint()
- Moving JSON-specific code from sql_yacc.yy to
  Type_handler_json_longtext::Column_definition_validate_check_constraint()

3. Adding new files sql_type_json.cc and sql_type_json.h
   and moving Type_handler+JSON related code into these files.

instant_alter_column_possible(): Add the other MDEV-17459 work-around
condition. The existence of fulltext indexes only prevents instant
DROP COLUMN or changing the order of columns. Other forms of instant
ALTER TABLE are no problem.

Before commit 4e7ee166 that merged
the MDEV-18295 fix from 10.3, the work-around of MDEV-17459 in
instant_alter_column_possible() was categorically refusing any
ALGORITHM=INSTANT if any FULLTEXT INDEX was present. After that commit,
a related condition was only present in prepare_inplace_alter_table_dict()
but not in the other callers of instant_alter_column_possible().

Fix some of the galera_sr suite test failures.
Remove tests that are not going to be run because required
feature is not supported.

	modified:   mysql-test/suite/galera_sr/disabled.def
	deleted:    mysql-test/suite/galera_sr/r/GCF-574.result
	modified:   mysql-test/suite/galera_sr/r/galera_sr_cc_slave.result
	modified:   mysql-test/suite/galera_sr/r/galera_sr_kill_all_norecovery.result
	modified:   mysql-test/suite/galera_sr/r/galera_sr_load_data.result
	deleted:    mysql-test/suite/galera_sr/r/galera_sr_sbr.result
	modified:   mysql-test/suite/galera_sr/r/mysql-wsrep-features#148.result
	deleted:    mysql-test/suite/galera_sr/r/mysql-wsrep-features#29.result
	deleted:    mysql-test/suite/galera_sr/t/GCF-574.test
	modified:   mysql-test/suite/galera_sr/t/galera_sr_cc_slave.test
	modified:   mysql-test/suite/galera_sr/t/galera_sr_kill_all_norecovery.cnf
	modified:   mysql-test/suite/galera_sr/t/galera_sr_kill_all_norecovery.test
	modified:   mysql-test/suite/galera_sr/t/galera_sr_load_data.test
	deleted:    mysql-test/suite/galera_sr/t/galera_sr_sbr.test
	modified:   mysql-test/suite/galera_sr/t/mysql-wsrep-features#148.test
	deleted:    mysql-test/suite/galera_sr/t/mysql-wsrep-features#29.test

dtype_is_string_type(), dtype_is_binary_string_type(),
dtype_is_non_binary_string_type(): Define as inline functions that
return bool, not ibool.

Also adjusted some test files.

The assertion happens under BACKUP STAGE BLOCK_COMMIT, when a DDL on a
temporary table (#sql-xxx) is found.

Apparently, assumption that all DDLs are blocked under FTWRL does not
hold for BACKUP STAGE, and temporary tables can still have ALTERs

The fix is to relax the assertion, and only check for opt_no_lock if
backup is *really* inconsistent, i.e either optimized DDL or CREATE/RENAME
are done on the tables that were not skipped during backup.

Allow ALGORITHM=INSTANT (or avoid touching any data)
when changing the collation, or in some cases, the character set,
of a non-indexed CHAR or VARCHAR column. There is no penalty
for subsequent DDL or DML operations, and compatibility with
older MariaDB versions will be unaffected.

Character sets may be changed when the old encoding is compatible
with the new one. For example, changing from ASCII to anything
ASCII-based, or from 3-byte to 4-byte UTF-8 can sometimes be
performed instantly.

This is joint work with Eugene Kosov.
The test cases as well as ALTER_CONVERT_TO, charsets_are_compatible(),
Type_handler::Charsets_are_compatible() are his work.
The Field_str::is_equal(), Field_varstring::is_equal() and
the InnoDB changes were mostly rewritten by me due to conflicts
with MDEV-15563.

Limitations:

Changes of indexed columns will still require
ALGORITHM=COPY. We should allow ALGORITHM=NOCOPY and allow
the indexes to be rebuilt inside the storage engine,
without copying the entire table.

Instant column size changes (in bytes) are not supported by
all storage engines.

Instant CHAR column changes are only allowed for InnoDB
ROW_FORMAT=REDUNDANT. We could allow this for InnoDB
when the CHAR internally uses a variable-length encoding,
say, when converting from 3-byte UTF-8 to 4-byte UTF-8.

Instant VARCHAR column changes are allowed for InnoDB
ROW_FORMAT=REDUNDANT, and for others only if the size
in bytes does not change from 128..255 bytes to more
than 256 bytes.

Inside InnoDB, this slightly changes the way how MDEV-15563
works and fixes the result of the innodb.instant_alter_extend test.
We change the way how ALTER_COLUMN_EQUAL_PACK_LENGTH_EXT
is handled. All column extension, type changes and renaming
now go through a common route, except when ctx->is_instant()
is in effect, for example, instant ADD or DROP COLUMN has
been initiated. Only in that case we will go through
innobase_instant_try() and rewrite all column metadata.

get_type(field, prtype, mtype, len): Convert a SQL data type into
InnoDB column metadata.

innobase_rename_column_try(): Remove the update of SYS_COLUMNS.

innobase_rename_or_enlarge_column_try(): New function,
replacing part of innobase_rename_column_try() and all of
innobase_enlarge_column_try(). Also changes column types.

innobase_rename_or_enlarge_columns_cache(): Also change
the column type.

move account options from LEX to Account_options structure
namely, mqh and ssl_*

Also, use LEX_CSTRING for ssl_*/x509_* strings and move
setting of ACL_USER::account_locked where it belongs

Add server support for user account locking.
This patch extends the ALTER/CREATE USER statements for
denying a user's subsequent login attempts:
  ALTER USER
    user [, user2] ACCOUNT [LOCK | UNLOCK]
  CREATE USER
    user [, user2] ACCOUNT [LOCK | UNLOCK]
The SHOW CREATE USER statement was updated to display the
locking state of an user.

Closes #1006

fix mysql_fix_privilege_tables to look for the `user` table in the
correct schema when deciding whether to convert it to `global_priv` table

make related tests a bit more verbose

Too easy to abuse. One tends to use it even when
microseconds are not needed and will be ignored.

Cleanup wsrep_schema and remove all references to wsrep_thd_pool

WSREP debug log levels support

* Removed all references related to wsrep_thd_pool (which was removed)

* Removed unused declarations in wsrep_schema.h

* The following would result invalid reads in
  Wsrep_schema::replay_transaction():
  ```
  frag_table->field[4]->val_str(&buf);

  Wsrep_schema_impl::end_index_scan(frag_table);
  Wsrep_schema_impl::finish_stmt(thd);
  ret= wsrep_apply_events(thd, rli, buf.c_ptr_safe(), buf.length());
  ```

  because `buf` was accessed after closing the table. The fix is to
  perform storage reads using a different THD.

* In Wsrep_schema::recover_sr_transactions(), cluster_table was opened
  for write, however it is only read here. And frag_table was opened
  for read, wereas write is potentially needed.
  Also, avoid copy caused by String::c_ptr() to zero terminate the c
  string, use c_ptr_quick instead.

Due to inconsistent usage of different cost models to calculate
the cost of ref accesses we have to make the calculation of the
gain promising by usage a range filter more complex.