Implement basic support for indexing function templates in

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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@112604 91177308-0d34-0410-b5e6-96231b3b80d8