[clang] Fix implementation of [temp.param]p14's first sentence. (PR #83487)

[Erich Keane via cfe-commits]

erichkeane wrote:

> The changes look correct to me, but I think we should add a DR test for this so that we can properly regenerate cxx_dr_status.html
> 
> Also, the changes should come with a release note.

Ooof, yeah, forgot the release note.  @Endilll has volunteered to do the DR test in a separate commit, as this only fixes the 1st half of the DR, so I'm not sure it actually fixes all of it.

https://github.com/llvm/llvm-project/pull/83487