Clean up the eager formatting API

[JonathanBrouwer]

For #151366 (comment)

Previously eager formatting worked by throwing the arguments into a diag, formatting, then removing the args again. This is ugly so instead we now just do the formatting completely separately.
This PR has nice commits, so I recommend reviewing commit by commit.

r? @GuillaumeGomez

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

rustc_errors::formatting was changed

cc @davidtwco, @TaKO8Ki

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to constck

cc @fee1-dead

rustc_macros::diagnostics was changed

cc @davidtwco, @TaKO8Ki

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

[JonathanBrouwer]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 48c772e (48c772ee3596abfd73f472d0115cdcd977f51de9, parent: a3ac2f21b3ae29145f587553efa8f76c16043777)

[rust-timer]

Finished benchmarking commit (48c772e): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (secondary 4.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.3%	[3.7%, 4.8%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

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

Binary size

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

Bootstrap: 481.299s -> 478.644s (-0.55%)
Artifact size: 395.15 MiB -> 395.10 MiB (-0.01%)

[JonathanBrouwer]

@bors r=GuillaumeGomez rollup

[rust-bors]

📌 Commit 7baf2be has been approved by GuillaumeGomez

It is now in the queue for this repository.