Track source information for template arguments and template specialization

Track source information for template arguments and template specialization
types.  Preserve it through template instantiation.  Preserve it through PCH,
although TSTs themselves aren't serializable, so that's pretty much meaningless.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@85500 91177308-0d34-0410-b5e6-96231b3b80d8