Improve diagnostics for an invalid binding in a tuple struct pattern

[JohnTitor]

This PR can be merged as is, but I think we could also add another branch that detects the case with PatKind::Ident(..) where .. is present and record it with a PartialRes::new(Res::Err), which should eliminate the second unnecessary error that complains about x not being defined. (Haven't looked at this deeply enough to be sure.)

Originally posted by @estebank in #74557 (comment)

Follow-up of #74557

[JohnTitor]

I'm going to close this issue as the above PR was reverted.
@estebank If you have any ideas for improving the diagnostics introduced by #74963, I'm happy to see another issue pointing it out <3