XA COMMIT and XA ROLLBACK operate on freed transaction object

The functions innobase_commit_by_xid() and innobase_rollback_by_xid(), which implement XA ROLLBACK and XA COMMIT for XA PREPARE transactions that are no longer attached to a connection, are freeing the transaction object to the pool prematurely, and then modifying the trx_t::in_depth and trx::in_innodb fields of the freed object. While the object is already free in the pool, it could be reused by trx_create_low() by some other connection. This could cause memory corruption and cause bugs like MDEV-14128 and MDEV-13935.

This bug was caught after adding AddressSanitizer poisoning to the transaction Pool.