Skip null checks where ANSI null-fallthrough still works

[deusaquilus]

Version: 3.0.2-SNAPSHOT
Module: quill-core
Database: all

In #1302, we introduced explicit null checks for Option operations exists, forall, map, and flatMap because when case statements were created inside, the ANSI null-fallthrough that was relied upon would not work correctly. Also, with the introduction of the Oracle module in #1295, string concatonation itself could not be relied upon to be ANSI-compliant (i.e. since Oracle does not have null-fallthrough for string concatonation).

The fact remains however, that whenever there is an instance of Option exists, forall, map, or flatMap, we only actually need to do explicit null-checking when a case statement (or non-ansi concat). Since extra null-checks make queries hard to understand, and decrease performance, it is worthwhile to actually check the body of exists, forall, map, or flatMap and see if there are case-statements or non-ansi concats inside and if there are not, fall back to the old behavior that relies on the ansi nulls.

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