librustdoc: return impl fmt::Display in more places instead of writing to strings

[yotamofek]

Continuation of #136784 , another attempt at landing the larger parts of #136748 .
I'd like to, gradually, make all of the building blocks for rendering docs in librustdoc return impl fmt::Display instead of returning Strings, or receiving a &mut String (or &mut impl fmt::Write). Another smaller end goal is to be able to get rid of write_str.
This PR is a large step in that direction.

Most of the changes are quite mechanical, and split up into separate commits for easier reviewing (hopefully). I took print_item and then started by converting all the functions it called (and their dependencies), and the last commit does the conversion for print_item itself. Ignoring whitespace should make reviewing a bit easier.

And most importantly, perf run shows pretty good results locally, hopefully CI will also show green 😁

r? @GuillaumeGomez , if you feel like it.

[lukas-code]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 1015ae9 with merge d331e3c...

[GuillaumeGomez]

Looks good to me, let's see what the benches will tell.

[bors]

☀️ Try build successful - checks-actions
Build commit: d331e3c (d331e3cd8e49b266010010bac60180ba08dc0c93)

[rust-timer]

Finished benchmarking commit (d331e3c): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-1.2%, -0.2%]	4
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	1
All ❌✅ (primary)	-0.6%	[-1.2%, -0.2%]	4

Max RSS (memory usage)

Results (primary 3.3%)

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)	3.3%	[3.3%, 3.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.3%	[3.3%, 3.3%]	1

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: 773.405s -> 773.68s (0.04%)
Artifact size: 361.04 MiB -> 361.04 MiB (0.00%)

[GuillaumeGomez]

Thanks!

@bors r+ rollup=never

[bors]

📌 Commit 1015ae9 has been approved by GuillaumeGomez

It is now in the queue for this repository.

[fmease]

Sorry but can you squash this? 28 commits is a bit excessive.

[fmease]

@bors r-

[yotamofek]

Sorry but can you squash this? 28 commits is a bit excessive.

Yeah, sure! One big commit then? Not really sure how to group it, otherwise

[fmease]

Either one big commit but one commit per file would be also be acceptable unless that makes no sense.

[yotamofek]

@fmease squashed into one commit

[fmease]

Thanks! @bors r=GuillaumeGomez

[bors]

📌 Commit 479116e has been approved by GuillaumeGomez

It is now in the queue for this repository.