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

[Erich Keane via cfe-commits]

erichkeane wrote:

> @erichkeane I added the following release note:
> 
> > Removed support for constructing on-stack `TemplateArgumentList`s. Interfaces should instead use `ArrayRef<TemplateArgument>` to pass template arguments.
> 
> I'm not entirely sure how to benchmark these changes. Perhaps I could determine the difference in AST memory usage compiling something like Boost or LLVM?

Boost is a great one I think, a memory profile of that would be great.  Even a 'rough' number (this decreased the memory pressure of compiling boost by 1.1%!) would be something good to 'show off'.

I think that is the good 'first half' of a release note, the second half giving justification for it (again, this both simplifies the code and decreases memory pressure by X% sorta thing)..

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