swift234

Iterative type checker: stub out "structural" type resolution requests.

Introduce a request kind for resolving a TypeRepr, and teach type
resolution the start of performing "structural" resolution of a
TypeRepr that gets the basic structure (e.g., we're pointing at
something that is a nominal type, etc.) without checking its
semantics, dealing with generic arguments, etc.

None of this is active yet.

Swift SVN r32569