Check fat pointer metadata compatibility modulo regions

[compiler-errors]

Regions don't really mean anything anyways during hir typeck.

If this erase_regions makes anyone nervous, it's probably equally valid to just equate the types using a type relation, but regardless we should not be using strict type equality while region variables are present.

Fixes #103384

[rust-highfive]

r? @eholk

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[eholk]

@bors r+

[bors]

📌 Commit 8333253 has been approved by eholk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 8333253 with merge 9cdfe03...

[bors]

☀️ Test successful - checks-actions
Approved by: eholk
Pushing 9cdfe03 to master...

[rust-timer]

Finished benchmarking commit (9cdfe03): comparison URL.

Overall result: ❌ regressions - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.6%, 1.0%]	7
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[0.6%, 1.0%]	7

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

Cycles

This benchmark run did not return any relevant results for this metric.

[lqd]

I'd think this is the bitmaps noise I expected to see when looking at today's results.

[compiler-errors]

Yeah, I think it's noise too. This erase_regions call I added is neither expensive nor hot.

[lqd]

bitmaps is currently being noisy

@rustbot label: +perf-regression-triaged