[libcxxabi] [llvm] [ItaniumDemangle] Unconditionally parse substitution template arguments (PR #131970)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> It looks like we might be able to make additional simplifications to the code since I think all meaningful references to TryToParseTemplateArgs are being removed in this patch?

There are still a couple there, and those ones do impact demangling (I ran the tests with them disabled and got failures).

https://github.com/llvm/llvm-project/pull/131970