- row_search_mvcc() should return DB_INTERRUPTED when it got killed.
- Add a syncpoint for the ICP check.
- Add test coverage for killed-during-ICP-check scenario

Backport of MDEV-22761 fixes for ICP from 10.4 commits:
* a6f95648
* c03885cd

XtraDB was fixed in deb3b9a1

Reviewer: Daniel Black