[AST] Directly store GTPD in TypeValueExpr

[Azoy]

Previously, TypeValueExpr stored a just built TypeRepr that we resolved in context in CSGen, but when we were in an extension context that concretized the generic parameter to something like 123, we would resolve it to this integer type instead of the archetype of that generic parameter. We relied on getting the archetype to return the underlying value type to treat the expression as, but with an integer type we are unable to retrieve that information back out. Instead, we always have the GTPD when making type value expressions (at least right now), so just store that directly and be a little less strict about requiring an ArchetypeType as our parameter type. An IntegerType is fine, SIL will properly optimize the instruction away if that's the case anyway.

Resolves: rdar://144818205

[Azoy]

@swift-ci please smoke test