rec_get_n_fields(): Add the parameter 'comp' for specifying the format.

rec_offs_make_valid(): Consistently use rec_offs_comp(offsets).

FIXME: fix crashes in innodb.instant_alter_null, main.function_defaults_innodb

The special flag REC_INFO_MIN_REC_FLAG used to be only set on the
first record in the leftmost node pointer page of each level of the tree.
It was never set on leaf pages.

MDEV-11369 Instant ADD COLUMN in MariaDB Server 10.3 repurposed the flag
to identify a hidden metadata record, which is stored in the first record
on the leftmost leaf page.

If the adaptive hash index points to records in the leftmost leaf page
after instant ALTER TABLE, we would have such a metadata record in the
table, an assertion could fail when trying to validate the index record.
In a release build, we might wrongly qualify the hidden metadata record
and thus return garbage results.

cmp_dtuple_rec_with_match_bytes(): If the REC_INFO_MIN_REC_FLAG is
set on the record, assert that this is the first record on the
leftmost page and that the record is a metadata record, and finally
return 1, because by definition, anything is greater than the
minimum record.

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.

rec_copy_prefix_to_buf(): If the page is in the flexible format,
convert the record to the original format, so that
btr_pcur_restore_position() will only have to deal with one format.
Merge the code from rec_copy_prefix_to_buf_old().

btr_pcur_restore_position_func(): Interpret a special value of
btr_cur_t::old_rec that points to the metadata record.

btr_cur_optimistic_insert(): Only insert the metadata record in the
newest format.

btr_cur_pessimistic_insert(): Allow the insertion of the metadata record.

page_copy_rec_list_end_to_created_page(): Reposition the cursor when
converting the page.

page_delete_rec_list_start(): Relax a too strict assertion.

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().

The dict_col_t::was_not_null() only matters for the clustered index,
not secondary indexes.

For dual-format pages, we must know whether columns were originally
NOT NULL, so that we can correctly interpret records in the old leaf
pages of the dual-format primary key index.

dict_table_t::init_instant(): Set the new DATA_WAS_NOT_NULL flags
and index->n_nullable based on it.

We want dict_index_t::n_nullable to reflect the original NOT NULL
state of the columns.

dict_table_t::init_instant(): Remove an assertion that would fail
when the InnoDB data dictionary is out of sync with the MariaDB
data dictionary. Correctly compute n_nullable. (With this,
the assertion ut_ad(index.n_nullable == n_nullable) at the
end of the function will fail.)

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.