[clang] Improve ast-dumper text printing of TemplateArgument

This improves and unifies our approach to printing all template
arguments.

The same approach to printing types is extended to all
TemplateArguments: A sugared version is printed in quotes,
followed by printing the canonical form, unless they would print
the same.

Special improvements are done to add more detail to template template
arguments.

It's planned in a future patch to use this improved TemplateName
printer for other places besides TemplateArguments.

Note: The sugared/desugared printing does not show up for
TemplateNames in tests yet, because we do a poor job of preserving
their type sugar. This will be improved in a future patch.