Merge new release of InnoDB 5.7.26 to 10.2

MySQL 5.7.26 includes the following InnoDB changes:

Applicable to MariaDB

Bug#27850600 INNODB ASYNC IO ERROR HANDLING IN IO_EVENT
This fixes incorrect error handling for the Linux libaio io_getevent().

Bug#29021730 CRASHING INNOBASE_COL_CHECK_FK WITH FOREIGN KEYS
There is no test case, and I failed to construct one. It looks like this bug could affect MariaDB.

Not applicable to MariaDB

Bug#29007731 ASSERTION FAILURE: FIL0FIL.CC.*SPACE->N_PENDING_FLUSHES == 0
This appears to be a follow-up fix to the MySQL counterpart of MDEV-18349. I was unable to repeat any assertion failures on MariaDB when running the following:

./mtr --big-test --parallel=auto --mysqld=--loose-innodb-flush-method=O_DIRECT_NO_FSYNC

The MySQL change is only removing debug assertions. I think that it is safe to keep those assertions for now, even if they could fail in MariaDB debug builds.

Bug#25966845 INSERT ON DUPLICATE KEY GENERATE A DEADLOCK
MariaDB already fixed much of this in MDEV-17073. This change conflicts with MDEV-17614 (which fixed the replication bug). MDEV-17603 would fix and re-enable statement-based replication.

Bug#28825718 - ASSERTION FAILURE: TRX0REC.CC:NNN:N_IDX > 0 WHILE DOING REPLACE/INSERT
This bug had already been fixed in MDEV-12004.

Bug #29207450 TINYTEXT COLUMN TAKES LONG TIME IN THE GROUP BY OPERATION
MDEV-11487 removed the code from MariaDB.

Bug#27373959 CREATE TABLE PANIC ON INNOBASE_PARSE_HINT_FROM_COMMENT
Already fixed in MDEV-15865.