MDEV-18224 MTR's internal check of the test case 'innodb.recovery_shutdown' failed due to extra #sql-ib*.ibd files

The test innodb.recovery_shutdown would occasionally fail,
because recovered incomplete transactions would be conflicting
with DROP TABLE, causing the background drop table queue to be invoked.

Add a slow shutdown before dropping the tables, so that the
recovered transactions will be rolled back. Starting with MDEV-14705,
normal shutdown would abort the rollback of recovered transactions.

Add test case for MDEV-18901 as MDEV-18967 and MDEV-18922 solves this issue

The file will be closed on line 540

Update system versioning fields before generated columns for left out
fill_record

Make buf_pool_t::io_buf_t() a more proper class.

buf_pool_t::io_buf_t::io_buf_t(): Silence the GCC 8 -Wclass-memaccess
warning for initializing slots[], which no longer is a plain old datatype
(POD) due to the std::atomic member.

trx_rseg_header_create(): Return the block descriptor, and
remove the redundant trx_rsegf_get_new() call. Apparently
the idea of that call was some kind of encapsulation or
abstraction, to discourage the direct use of the constant TRX_RSEG.

This also removes the trx_purge_initiate_truncate() local
variable rseg_header, which was only used in debug builds.

Tests for MDEV-18892 failed, because of extra 'Prepare' and 'Close stmt'
entries in the output.

Filtering out PS related entries (where it is necessary).

Field::is_equal(): treat old type and new one without AUTO_INCREMENT as equal

Closes #1208

let mysql_upgrade to work even when innodb_index_stats or
innodb_table_stats are missing.

(mysql_upgrade knows to ignore "unknown table" errors)

row_ins_foreign_fill_virtual(): Construct update->old_vrow
with ROW_COPY_DATA instead of ROW_COPY_POINTERS. With the latter,
the object would be pointing to a buffer pool page frame. That page
frame can become stale and invalid as soon as
row_ins_foreign_check_on_constraint() invokes mtr_t::commit().

Most of the time, the pointer target is not going to be overwritten
by anything, and everything appears to work correctly.
Buffer pool page replacement is highly unlikely, and any pessimistic
operation that would overwrite the old location of the record is only
slightly more likely. It is not known whether there is an actual bug.
This came up while diagnosing MDEV-18879 in MariaDB 10.3.

row_ins_foreign_check_on_constraint(): When constructing
cascade->historical_row for tables WITH SYSTEM VERSIONING,
use the appropriate mode ROW_COPY_DATA, because the pointers
will be stale after mtr_commit() is invoked.

Adding an intermediate volatile variable to avoid using co-processor registers
on some platforms (e.g. 32-bit x86).
This change makes test results stable accross all platforms.

The MDEV-17262 commit 26432e49
was skipped. In Galera 4, the implementation would seem to require
changes to the streaming replication.

In the tests archive.rnd_pos main.profiling, disable_ps_protocol
for SHOW STATUS and SHOW PROFILE commands until MDEV-18974
has been fixed.

Access purge_sys.rseg directly, instead of obscuring it with a parameter.

MariaDB Server 10.0 and 10.1 support non-indexed virtual columns,
which are hidden from the storage engine. Starting with MDEV-5800
in MariaDB 10.2.2, the virtual columns are visible to storage engines.

calc_row_difference(): Follow up the MDEV-17199 fix, which forgot
to increment num_v when skipping virtual columns in tables that
were created before MariaDB 10.2.2. This caused a corruption of
the update vector when an updated persistent column is preceded
by virtual columns.

The macro innobase_is_v_fld() turns out to be equivalent with
the opposite of Field::stored_in_db(). Remove the macro and
invoke the member function directly.

innodb_base_col_setup_for_stored(): Simplify a condition to only
check Field::vcol_info.

innobase_create_index_def(): Replace some redundant code with
DBUG_ASSERT().

MariaDB before MDEV-5800 in version 10.2.2 did not support
indexed virtual columns. Non-persistent virtual columns were
hidden from storage engines. Only starting with MDEV-5800, InnoDB
would create internal metadata on virtual columns.

On TRUNCATE TABLE, an old .frm file from before MDEV-5800 may be
used as the table schema. When the table is being re-created by
InnoDB, the old schema must be used. That is, we may hide
the existence of virtual columns from InnoDB.

create_table_check_doc_id_col(): Remove the assertion that failed.
This function can actually correctly deal with virtual columns
that could have been created before MariaDB 10.2.2 introduced MDEV-5800.

create_table_info_t::create_table_def(): Do not create metadata for
virtual columns if the table definition was created before MariaDB 10.2.2.

This bug was introduced by MDEV-12288, which made InnoDB use
a single undo log for persistent transactions, instead of
maintaining separate insert_undo and update_undo logs.

trx_undo_reuse_cached(): Initialize the TRX_UNDO_PAGE_TYPE
after reusing a cached undo log page for undo log.
Failure to do so can cause trx_undo_mem_create_at_db_start()
to misclassify new undo log records as TRX_UNDO_INSERT.
This in turn would trigger an assertion failure in
trx_roll_pop_top_rec_of_trx() due to undo==insert.