Remove RegionExt; move methods to Region in rustc_type_ir

[Jamesbarford]

Removes RegionExt from rustc_middle with all methods on Region.

Some changes I think are worth pointing out (of which are all in the first commit -> f949bb7) ;

• Changed the signature of Region::new_late_param to accept a I::LateParamRegion where previously it was able to construct a LateParamRegion from some method parameters.

added to interner:

• fn span_delayed_bug(self, span: Self::Span, msg: impl ToString) -> Self::ErrorGuaranteed; which could be useful elsewhere when porting things across to rustc_type_ir
• fn generics_of_early_param_region_def_id(self, def_id: Self::DefId, ebr: Self::EarlyParamRegion) -> Self::DefId; which is quite nasty but calling generics_of returned another type that I would have possibly create a trait for which felt more messy.
• fn get_re_var_lifetime(self, var_idx: usize) -> Option<Region<'tcx>> need to get a region in Region::new_var.

traits added to inherent

• RegionName so we can get the names of LateParamRegion and EarlyParamRegion with a get_name() and also is_named().
• DefIdGetter so we can get the DefId of kind in LateParamRegion

r? lcnr

Part of #159654

[rustbot]

HIR ty lowering was modified

cc @fmease

[lcnr]

generics_of_early_param_region_def_id

hmm, without looking much at the code, I feel like we should move Generics into rustc_type_ir instead 🤔 how much effort is that/actually make it an inherent trait to make that transition easier in the future

[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 #160627) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.