fix REGEXP_LIKE, CONTAINS_STRING, ICONTAINS_STRING for correct 3vl behavior

[clintropolis]

Description

Fixes regexp_like, contains_string, and icontains_string to return null instead of false in SQL compatible null handling mode to have correct three-value logic behavior. I did not put this behavior behind a flag, though if we are worried about the bug fix changing behavior I suppose we could associate it with NullHandling.useThreeValueLogic(), though kind of weird since that is currently tied to use for native filters, or ExpressionProcessing.useStrictBooleans() which traditionally controls the other expression related 3vl stuff.

Release note

REGEXP_LIKE, CONTAINS_STRING, and ICONTAINS_STRING correctly return null for null value inputs in SQL compatible null handling mode (the default configuration).

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This PR has:

• been self-reviewed.
• a release note entry in the PR description.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• been tested in a test Druid cluster.

[abhishekagarwal87]

let's put it behind one of these feature flags, please :) My experience is that long-time users often adjust to this weird behavior and then complain about their workflows breaking.

[clintropolis]

let's put it behind one of these feature flags, please :) My experience is that long-time users often adjust to this weird behavior and then complain about their workflows breaking.

The problem is that neither of these feature flags seem very appropriate. druid.generic.useThreeValueLogicForNativeFilters definitely seems not right because it has 'native filters' in the name. druid.expressions.useStrictBooleans also doesn't really feel right because the primary thing that config does is make 'LONG' be the standard boolean type, instead of a mix of boolean-ish types. It by side-effect has some three-value logic stuff that it fixed with AND and OR filters, but doesn't fully control SQL compatible three-value logic behavior for the rest of expressions, for the most part, that just happens by default if druid.generic.useDefaultValueForNull=false.

I'm pretty strongly opposed to adding yet another feature flag for a bug fix, it isn't really sustainable. This fix already only has any effect if druid.generic.useDefaultValueForNull=false...

[abhishekagarwal87]

LGTM. The SQL compatibility feature flag is good enough.