Create a NOT_MATCHES_REGEX module operator

[John]

It would enhance users' editing experience if developers could create a module field to conditionally show if a controlling field's value does not match a regex. For example, show a module field only if a controlling text field does not contain the string "foo" (it would hide for foo, food, foodie, etc).

Currently negative lookahead does not work in the MATCHES_REGEX visibility operator. For example, the following regex does not work:

(?!hello)

This is according to re2 documentation.

(?!re)

before text not matching re (NOT SUPPORTED)

I propose we add a NOT_MATCHES_REGEX operator in order to work around re2's limitations.