This is the meat of the code to add Clang modules
support to LLDB. It includes the following:
- Changed DeclVendor to TypeVendor.
- Made the ObjCLanguageRuntime provide a DeclVendor rather than a TypeVendor.
- Changed the consumers of TypeVendors to use DeclVendors instead.
- Provided a few convenience functions on ClangASTContext to make that easier.