Add File constructors that return files wrapped with a buffer

[cuviper]

In addition to the light convenience, these are intended to raise visibility that buffering is something you should consider when opening a file, since unbuffered I/O is a common performance footgun to Rust newcomers.

ACP: rust-lang/libs-team#446
Tracking Issue: #130804

[rustbot]

r? @ChrisDenton

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[joshtriplett]

@bors r+

[bors]

📌 Commit 458537e has been approved by joshtriplett

It is now in the queue for this repository.

[bors]

⌛ Testing commit 458537e with merge 4c62024...

[bors]

☀️ Test successful - checks-actions
Approved by: joshtriplett
Pushing 4c62024 to master...

[rust-timer]

Finished benchmarking commit (4c62024): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -perf-regression

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
Regressions ❌ (secondary)	1.4%	[1.3%, 1.4%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

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

Cycles

Results (primary 0.7%)

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)	0.7%	[0.5%, 1.1%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[0.5%, 1.1%]	5

Binary size

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

Bootstrap: 769.688s -> 771.199s (0.20%)
Artifact size: 340.87 MiB -> 340.88 MiB (0.00%)

[RalfJung]

This seems incomplete, since it can also return an error from try_new_buffer?

[cuviper]

Sure, see #131462.