Also, related to MDEV-15522, MDEV-17304, MDEV-17835,
remove the Galera xtrabackup tests, because xtrabackup never worked
with MariaDB Server 10.3 due to InnoDB redo log format changes.

Disable tests that do not yet pass.

dict_create_add_foreigns_to_dictionary(): Do not commit the transaction.
The operation can still fail in dict_load_foreigns(), and we want
to be able to roll back the transaction.

create_table_info_t::create_table(): Never reset m_drop_before_rollback,
and never commit the transaction. We use a single point of rollback
in ha_innobase::create(). Merge the logic from
row_table_add_foreign_constraints().

btr_pcur_store_position(): Merge the code from
dict_index_copy_rec_order_prefix().

This is a regression due to MDEV-17816.

When creating a table fails, we must roll back the dictionary
transaction. Because the rollback may rename tables, and because
InnoDB lacks proper undo logging for CREATE operations, we must
drop the incompletely created table before rolling back the
transaction, which could include a RENAME operation.
But, we must not blindly drop the table by name; after all,
the operation could have failed because another table by the
same name already existed.

create_table_info_t::m_drop_before_rollback: A flag that is set
if the table needs to be dropped before transaction rollback.

create_table_info_t::create_table(): Remove some duplicated
error handling.

ha_innobase::create(): On error, only drop the table if it was
actually created.

Added a testcase

MDEV-17854 Assertion `decimals <= 6' failed in my_time_fraction_remainder on SELECT with NULLIF and FROM_UNIXTIME on incorrect time

The code became unused in commit 10590dd3.

Added support for usual agreggate UDF (UDAF)
Added remove() call support for more efficient window function processing
Added example of aggregate UDF with efficient windows function support

Add check that file key management plugin is found.

fil_space_t::add(): Replaces fil_node_create(), fil_node_create_low().
Let the caller pass fil_node_t::handle, to avoid having to close and
re-open files.

fil_node_t::read_page0(): Refactored from fil_node_open_file().
Read the first page of a data file.

fil_node_open_file(): Open the file only once.

srv_undo_tablespace_open(): Set the file handle for the opened
undo tablespace. This should ensure that ut_ad(file->is_open())
no longer fails in recv_add_trim().

xtrabackup_backup_func(): Remove some dead code.

xb_fil_cur_open(): Open files only if needed. Undo tablespaces
should already have been opened.

trx_assign_rseg_low(): Skip dedicated undo tablespaces if
innodb_undo_tablespaces=0 has been set after the database was created.

When dropping a partially created table due to failure,
use SQLCOM_TRUNCATE instead of SQLCOM_DROP_DB, so that
no foreign key constraints will be touched. If any
constraints were added as part of the creation, they would
be reverted as part of the transaction rollback.

We need an explicit call to row_drop_table_for_mysql(),
because InnoDB does not do proper undo logging for CREATE TABLE,
but would only drop the table at the end of the rollback.
This would not work if the transaction combines both
RENAME and CREATE, like TRUNCATE now does.

MDEV-17831 Assertion `supports_instant()' failed in dict_table_t::prepare_instant upon ADD COLUMN on table with KEY_BLOCK_SIZE

dict_table_t::prepare_instant(): Remove too strict assertions that
could fail if the MariaDB and InnoDB data dictionaries are out of sync.

That the dictionaries got out of sync during TRUNCATE TABLE
is a separate bug was fixed in 10.2 by
commit 971e1d86.

If a table had a KEY_BLOCK_SIZE attribute, but no ROW_FORMAT,
it would be created as ROW_FORMAT=COMPRESSED in InnoDB.
However, TRUNCATE TABLE would lose the KEY_BLOCK_SIZE attribute
and create the table with the innodb_default_row_format (DYNAMIC).

This is a regression that was introduced by MDEV-13564.

update_create_info_from_table(): Copy also KEY_BLOCK_SIZE.

The test galera_sst_mariabackup_table_options was disabled,
because the server refuses to start up due to wrong parameters.

The error handling in the MDEV-13564 TRUNCATE TABLE was broken
when an error occurred during table creation.

row_create_index_for_mysql(): Do not drop the table on error.

fts_create_one_common_table(), fts_create_one_index_table():
Do drop the table on error.

create_index(), create_table_info_t::create_table():
Let the caller handle the index creation errors.

ha_innobase::create(): If create_table_info_t::create_table()
fails, drop the incomplete table, roll back the transaction,
and finally return an error to the caller.

lock_rec_queue_validate(): Assert page_rec_is_leaf(rec), except when
the record is a page infimum or supremum.

lock_rec_validate_page(): Relax the assertion that failed.
The assertion was reachable when the record lock bitmap was empty.

lock_rec_insert_check_and_lock(): Assert page_is_leaf().

Several race conditions between MDEV-15562 instant ALTER TABLE and purge
were observed.

The most obvious race condition resulted in a reported assertion failure in
dict_index_t::instant_add_field(): instant.n_core_fields == n_core_fields
would not hold if the table was emptied by purge after the time
dict_table_t::prepare_instant() was called.

During purge, it can turn out that the table is logically empty, only
containing a metadata record. If the metadata record is of the type
created by MDEV-11369 instant ADD COLUMN, it can be removed and
dict_index_t::clear_instant_add() can be called. This will convert the
table to the canonical non-instant format. (If the metadata record is
of the MDEV-15562 type, then it can only be deleted if the table becomes
empty as the result of rollback of an instant ALTER TABLE operation.)

row_purge_remove_clust_if_poss_low(): Add a debug check that ensures
that purge can never remove a MDEV-15562 metadata record.

ha_innobase::open(): Add a comment about the necessity of rolling
back any recovered instant ALTER TABLE transaction on the table.

instant_metadata_lock(): An auxiliary function to acquire a page latch
on the metadata record, to prevent race conditions.

dict_table_t::prepare_instant(), dict_index_t::instant_add_field(),
dict_table_t::rollback_instant(), innobase_instant_try():
Invoke instant_metadata_lock() in order to prevent race conditions.

dict_index_t::instant_add_field(): Correct debug assertions.
The == was guaranteed by code in dict_table_t::prepare_instant()
that was introduced in MDEV-15562. Due to the race condition,
we could occasionally have <=, but never >= like the code was
after MDEV-11369.

ha_innobase_inplace_ctx::instant_column(): Wrapper for
dict_table_t::instant_column(). Add debug assertions.

Replace table->space->id with table->space_id.

MDEV-17804: Galera tests cause mysql_socket.h:738: inline_mysql_socket_send: Assertion `mysql_socket.fd != -1' failed.

Do not do end of statement logic if thd is already killed as
socket is already closed.