Implement basic support for indexing function templates in

libclang. This includes:
  - Cursor kind for function templates, with visitation logic
  - Cursor kinds for template parameters, with visitation logic
  - Visitation logic for template specialization types, qualified type
  locations
  - USR generation for function templates, template specialization
  types, template parameter types.

Also happens to fix PR7804, which I tripped across while testing.

llvm-svn: 112604