[clang] [clang][Parser] "Better" error messages for invalid template template (PR #95726)

[via cfe-commits]

Veeloxfire wrote:

> Also, this needs a release note (in `clang/docs/ReleaseNotes.rst`, probably in the section ‘Improvements to Clang’s Diagnostics’ or whatever it was called).

So I dont end up making 100 commits rewording this:
How about "Clang now diagnoses template template paramter missing `<` as typo for `typename`"

https://github.com/llvm/llvm-project/pull/95726