#2794 adding tests verifying the regression, `DateTimeImmutable` should STILL work, even if unintentionally

Since it was deprecated.

If you pass a null to the where array of update or delete it's
pretty obvious what you want.

Most (all?) databases won't match anything if you actually try
to compare with NULL making this a silent failure without it.

1. Reworked the parser syntax to use proper Oracle escaping syntax as '' instead of \'.
2. Moved valid tests to the Functional section to ensure correct SQL syntax and logic.

Closes #1882

#2704 - Removed hacky handling of error handler restore operations - restoring twice in the test instead

primary key on MySQL platform.

Default isolation level on mysql is REPEATABLE READ

https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_tx_isolation