Convert to inline diagnostics in rustc_parse

[JonathanBrouwer]

This was the most annoying one by far, had to make a few changes to the representation of two errors (no user-facing changes tho), these changes are in separate commits for clarity :)

For #151366
r? @jdonszelmann

[rustbot]

rustc_macros::diagnostics was changed

cc @davidtwco, @TaKO8Ki

[jdonszelmann]

r=me after you looked at that :)

View changes since this review

[jdonszelmann]

If this is such a common operation, why don't we have PSess::empty(). That might be nicer actually

[JonathanBrouwer]

I thought about it, but in a few days after the other crates are translated I can just remove the argument from PSess::new entirely, so not worth the effort

[JonathanBrouwer]

@jdonszelmann I accidentally broke the unstable -Ztranslate-additional-ftl option. This option can be used to override translation messages. This is already broken on nightly, it's just that the only test using this option happened to use rustc_parse.

I should be able to repair this with a little bit of effort, might take me a few days and this PR is very brittle, so would prefer to do this in a separate PR. I added this to the tracking issue so it is not forgotten. You can r+ if you agree with this approach

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-bors]

☔ The latest upstream changes (presumably #152264) made this pull request unmergeable. Please resolve the merge conflicts.