[clang] [clang] require template arg list after template kw (PR #80801)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Thank you for this! The changes should also come with a release note in clang/docs/ReleaseNotes.rst so users know about the change.

https://github.com/llvm/llvm-project/pull/80801