[python bindings] Expose getNumTemplateArguments

Expose the C bindings for clang_Type_getNumTemplateArguments() and
clang_Type_getTemplateArgumentAsType() in the python API.

Patch by kjteske (Kyle Teske).

Reviewed By: jbcoe

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D51299

llvm-svn: 341930