Based on a contributed patch from Jerome Brauge.

MDEV-12098 sql_mode=ORACLE: Implicit cursor FOR loop

Implementing cursor%ROWTYPE variables, according to the task description.

This patch includes a refactoring in how sp_instr_cpush and sp_instr_copen
work. This is needed to implement MDEV-10598 later easier, to allow variable
declarations go after cursor declarations (which is currently not allowed).

Before this patch, sp_instr_cpush worked as a Query_arena associated with
the cursor. sp_instr_copen::execute() switched to the sp_instr_cpush's
Query_arena when executing the cursor SELECT statement.

Now the Query_arena associated with the cursor is stored inside an instance
of a new class sp_lex_cursor (a LEX descendand) that contains the cursor SELECT
statement.

This simplifies the implementation, because:
- It's easier to follow the code when everything related to execution
  of the cursor SELECT statement is stored inside the same sp_lex_cursor
  object (rather than distributed between LEX and sp_instr_cpush).
- It's easier to link an sp_instr_cursor_copy_struct to
  sp_lex_cursor rather than to sp_instr_cpush.
- Also, it allows to perform sp_instr_cursor_copy_struct::exec_core()
  without having a pointer to sp_instr_cpush, using a pointer to sp_lex_cursor
  instead. This will be important for MDEV-10598, because sp_instr_cpush will
  happen *after* sp_instr_cursor_copy_struct.

After MDEV-10598 is done, this declaration:

DECLARE
  CURSOR cur IS SELECT * FROM t1;
  rec cur%ROWTYPE;
BEGIN
  OPEN cur;
  FETCH cur INTO rec;
  CLOSE cur;
END;

will generate about this code:

+-----+--------------------------+
| Pos | Instruction              |
+-----+--------------------------+
|   0 | cursor_copy_struct rec@0 | Points to sp_cursor_lex through m_lex_keeper
|   1 | set rec@0 NULL           |
|   2 | cpush cur@0              | Points to sp_cursor_lex through m_lex_keeper
|   3 | copen cur@0              | Points to sp_cursor_lex through m_cursor
|   4 | cfetch cur@0 rec@0       |
|   5 | cclose cur@0             |
|   6 | cpop 1                   |
+-----+--------------------------+

Notice, "cursor_copy_struct" and "set" will go before "cpush".
Instructions at positions 0, 2, 3 point to the same sp_cursor_lex instance.

The bug was introduced in the patch for "MDEV-10597 Cursors with parameters".
The LEX created in assignment_source_expr was not put into
thd->lex->sphead->m_lex (the stack of LEX'es), so syntax error in "expr"
caused a wrong memory cleanup in sp_head::~sp_head().

The fix changes the code to use sp_head::push_lex() followed by
sp_head::restore_lex(), like it happens in all other similar cases.

Allowing qualified procedure names to be used without the CALL keyword:

BEGIN
  test.p1(10);
  test.p2;
END;

Note:
- COMMIT and ROLLBACK cannot be used in a direct assignment anymore:
    COMMIT:= 10;
    ROLLBACK:= 10;
  But as they are reserved keywords in Oracle anyway, this is not a problem.
- SHUTDOWN now also cannot be used in direct a direct assignment:
    SHUTDOWN:=10;
  If this causes migration problems in the future, the grammar should
  be modified.

Note:
  Variables with names COMMIT, ROLLBACK and SHUTDOWN can still be assigned
  with the SET statement, e.g. SET COMMIT=10;

MDEV-12088 sql_mode=ORACLE: Do not require BEGIN..END in multi-statement exception handlers in THEN clause

This is covered in mysql-test/t/variables.test. There is no sense
to test this for every individual variables.

This is to reduce the coming soon patch for ROW-type routine variables,
which will change the error from ER_PARSE_ERROR to a new error
"unknown structured variable".

Now when sql_mode=ORACLE, the concatenation operator || treats
NULLs as empty strings.

Based on the contributed patch from Jérôme Brauge.

This fixes compat/oracle.sp test failure in release builds.

Part 2:

Moving the part of Sql_condition that contain condition items
(such as m_class_origin, m_cursor_name, etc) into a separate
class Sql_condition_items. This allows to remove duplicate code in
different Sql_condition constructors.

Also, introducing new Sql_condition constructors and removing the method
Sql_condition::set(). All code sequences that called an Sql_condition
constructor followed by Sql_condition::set() are now replaced to
the new constructor calls. This gives light performance improvement,
as the relevant members are now initialized only one time.

An additional change for "Part 9: EXCEPTION handlers"

This construct:
  EXCEPTION WHEN OTHERS THEN ...;
now catches warning-alike conditions, e.g. NO_DATA_FOUND.

MDEV-10867 PREPARE..EXECUTE is not consistent about non-ASCII characters

Adding Oracle specific tests

A fix for MDEV-10411 Providing compatibility for basic PL/SQL constructs (Part 6: Assignment operator)

Fixed that a crash in this script:

SET sql_mode=ORACLE;
max_sort_length:= 1024;

Fixed that EXPLAIN EXTENDED erroneously returned
"SQL%%ROWCOUNT" instead of "SQL%ROWCOUNT"

Adding Oracle-specific tests for stored functions as EXECUTE..USING parameters.

Adding Oracle specific tests

Adding Oracle specific tests

Adding the Oracle style DECODE function:

  DECODE(operand, search, result [, search, result ...] [, default_result])

MDEV-10596 Allow VARCHAR and VARCHAR2 without length as a data type of routine parameters and in RETURN clause