Push nested-name-specifier source location information into template

template arguments. I believe that this is the last place in the AST
where we were storing a source range for a nested-name-specifier
rather than a proper nested-name-specifier location structure. (Yay!)

There is still a lot of cleanup to do in the TreeTransform, which
doesn't take advantage of nested-name-specifiers with source-location
information everywhere it could.

llvm-svn: 126844