Fix known issue with Any, Any resolution

[brynrhodes]

The following expressions:

define Test1: null ~ null
define Test2: null = null

result in an error about ambiguous resolution. This is because the generic resolution that would have enabled these is disabled (see #420) because once a binary operator signature for Any, Any is instantiated, it ends up being used for all resolutions, even if a more appropriate specific resolution is available. The operator resolution needs to take this possibility into account so that this functionality can be reintroduced.

[cmoesel]

This is only relevant when both sides are literal null, right? In other words, while this might come up in test cases, you should never see production CQL that does a comparison between two literal nulls -- so it's really only a problem for tests cases like the one above, right?

[brynrhodes]

Yes, it's an edge case for sure, but there are also places where it will manifest if you only have a compile-time type of Any, where an =(Any, Any) should be allowed but the translator can't resolve it.

[JPercival]

Should retest this with the latest operator resolution code. Might be resolved as it recently got smarter.