Make clearer that guarantees in ABI compatibility are for Rust only

[Mark-Simulacrum]

cc #132136 (comment) -- it looks like we already had a note that I missed in my initial look here, but this goes further to emphasize the guarantees, including uplifting it to the top of the general documentation.

r? @RalfJung

[RalfJung]

LGTM, thanks
Cc @rust-lang/opsem for awareness.

@bors r+ rollup

[bors]

📌 Commit c1a08f9 has been approved by RalfJung

It is now in the queue for this repository.

[bors]

⌛ Testing commit c1a08f9 with merge 5d0b6ab...

[rust-log-analyzer]

The job x86_64-apple-2 failed! Check out the build log: (web) (plain)

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[jieyouxu]

Job was cancelled.
@bors r=@RalfJung

[bors]

📌 Commit c1a08f9 has been approved by RalfJung

It is now in the queue for this repository.

[bors]

⌛ Testing commit c1a08f9 with merge 6929a48275547ef2aae72b85b5b5d8e4acbb5067...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 6929a48 to master...

[rust-timer]

Finished benchmarking commit (6929a48): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

Max RSS (memory usage)

Results (primary -1.4%, secondary -0.9%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-1.4%	[-1.4%, -1.4%]	1
Improvements ✅ (secondary)	-1.8%	[-3.0%, -1.0%]	4
All ❌✅ (primary)	-1.4%	[-1.4%, -1.4%]	1

Cycles

Results (secondary -2.9%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-3.3%, -2.4%]	9
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 783.63s -> 783.592s (-0.00%)
Artifact size: 333.67 MiB -> 333.70 MiB (0.01%)