swift234

Reflection: Type lowering for metatypes

The thin vs thick distinction is handled a little awkwardly. Instead of
passing around abstraction patterns, we add a "must be thick" bit to
MetatypeTypeRef, and thicken substitutions (to handle T; T := C.Type)
and the result of a subtitution (to handle T.Type; T := C).

With the exception of enums this completes <rdar://problem/25738849>.