Streamify getNameForDiagnostic and remove the string versions of PrintTemplateArgumentList.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175894 91177308-0d34-0410-b5e6-96231b3b80d8
Streamify FormatASTNodeDiagnosticArgument.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175895 91177308-0d34-0410-b5e6-96231b3b80d8