[clang] [clang] Improve ast-dumper text printing of TemplateArgument (PR #93431)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> Should we also be updating JSONNodeDumper.cpp at the same time?

We would ideally update it as well.

Not necessarily in the same PR, as it's a separate change that doesn't need to be synchronized.

It's just not important to me, because I don't personally use the JSON dumper for debugging.

https://github.com/llvm/llvm-project/pull/93431