Implement crash-safe execution the user XA on binlog-less slave

This task is ensued by MDEV-742 and implements the 2nd part of the upstream's
Bug#76233, see MDEV-21469 for the 1st part.

XA Commit, Rollback and XA PREPARE execution on slave involves mysql.gtid_slave_pos update to indicate the slave execution status.
Unlike the regular transaction, that update can't be executed within the replicated XA.

It has to be processed as a separate transaction to be two-phase-committed with the replicated one.
Specifically, in the XA-PREPARE case the mysql.gtid_slave_pos transaction gains a special xid that 'matches' the xid of the user one. It prepares "in parallel" with the replicated XA and when the latter prepare OKs, it commits.
In case of a crash in between recovery will search for all user prepared trx:s, and try to match
their xid:s. mysql.gtid_slave_pos trx that matches a user XA allows for accounting the user XA prepare as successful and mysql.gtid_slave_pos one then commits.

Similar method is applied to XA-COMMIT,ROLLBACK.