I introduce AnyEqualsExpr for either reference or value equality and AnyEqualityTest for the same concept including not-equals operators, and use them wherever the written QL clearly doesn't care about the difference between reference and value comparison, typically because it is concerned with testing against null or against a primitive constant.
We might want to unify some of these in future, but doing that
correctly is easier than splitting them up correctly, so I've given each
one its own QL class for now.
I am not familiar with many of the libraries/queries that use CastExpr.
I've briefly looked at them and updated them in a way that looks
superficially reasonable, but some of the uses will probably want to be
refined later.
