Implement the ObjC pseudo built-in types as clang "BuiltinType's". I say pseudo built-in types, since Sema still injects a typedef for recognition (i.e. they aren't truly built-ins from a parser perspective).

This removes the static data/methods on ObjCObjectPointerType while preserving the nice API (no need to fiddle with ASTContext:-).

This patch also adds Type::isObjCBuiltinType().

This should be the last fairly large patch related to recrafting the ObjC type system. The follow-on patches should be fairly small.

llvm-svn: 75808