Remove reference map from another set of midend passes

[asl]

This includes less obvious cases. Plus some additional cleanup.

[asl]

Two issues were uncovered so far:

• DPDK backend has pass (DismantleMuxExpression) that relies on fresh refmap, but does not rebuild it. The code before PR is already problematic and worked by coincidence :)
• BMV2 PSA midend uses custom local copy propagation policy that relies on fresh external reference map (like "global variable"), so we really need to have refmap current there before local_copyprop.

Overall I think eventually we'd need passes to maintain their own copy of reference map if they really need it; we should not have global refmap object passed everywhere as maintaining its freshness is non-trivial and error-prone.

[ChrisDodd]

Shouldn't this be DoConstantFolding() : DoConstantFolding(this, nullptr) {}

[asl]

There is one very subtle but important difference. We do use refmap in absence of typemap during constfolding of path expressions. However, this requires more or less complete IR. This is not the case for P14-to-16 conversion, where constfolding is done in the middle of conversion and therefore we just crash not being able to resolve anything.

On the other hand, it seems we're missing some constfolding opportunities if we'd require known types along with resolution contex.

Things are a bit messy, yes, I am planning to untangle this eventually.