Merge MySQL 5.7.19

https://github.com/percona/percona-server/pull/1892

Merge MySQL 5.7.19.

Verify upstream fixes and revert ours for:
- bug 1677130 / https://bugs.mysql.com/bug.php?id=85678
- bug 1604462 / https://bugs.mysql.com/bug.php?id=82283
- bug 1604774 / https://bugs.mysql.com/bug.php?id=82307 (keep our fix for bug 1676847)
- bug 1617150 / Oracle's Internal Bug #18950197
- bug 1660591 / https://bugs.mysql.com/bug.php?id=85088 + https://bugs.mysql.com/bug.php?id=84736 (?) + https://bugs.mysql.com/bug.php?id=84451 (?) + Oracle's Internal Bug #25369742

Add testcases for: 83816/84658/81449 (missed in 5.7.18; probably a single testcase is enough),
84656, 84640
84824, 82967
86799