Add a pass to flag arrays only differing in tags

@majosm reported a situation where a large compile time difference was observed based on an array having a tag vs. not. This is plausible, as even different just tags can lead to arrays not being viewed as equal and therefore failing to be merged in common subexpression elimination. This means that this value (and all its dependents, if both versions are used) are computed multiple times. If multiple uses of the pattern occur, then this could lead to exponential growth of DAG size.

All of this is likely almost always unintended, and so we should at least warn about it (if not error). What I have in mind is a pass that strips all tags and flags the situation in which that process produces multiple versions of the same array that compare equal after stripping.