[clang] [Clang][NFC] Remove TemplateArgumentList::OnStack (PR #79760)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

So I like this!  I think it is a good change.  I WOULD like to see a release note.  I know this isn't particularly 'user visible', but I think, paired with some sort of benchmark, that this would be useful to brag about.

We often run out of stack space while instantiating templates that are particularly large/deep despite our best efforts, and I have a feeling that both saving space in the TAL plus not storing anythign on the stack would improve that.

@cor3ntin : FYI, this would be interesting to be aware of.  Comments on how a release note could go are also appreciated.

https://github.com/llvm/llvm-project/pull/79760