Fix rustc_parse_format spans following escaped utf-8 multibyte chars

[Alexendoo]

Currently too many skips are created for char escapes that are larger than 1 byte when encoded in UTF-8, playground:

fn main() {
    format!("\u{df}{a}");
    format!("\u{211d}{a}");
    format!("\u{1f4a3}{a}");
}

error[[E0425]](https://doc.rust-lang.org/stable/error-index.html#E0425): cannot find value `a` in this scope
 --> src/main.rs:2:22
  |
2 |     format!("\u{df}{a}");
  |                      ^ not found in this scope

error[[E0425]](https://doc.rust-lang.org/stable/error-index.html#E0425): cannot find value `a` in this scope
 --> src/main.rs:3:25
  |
3 |     format!("\u{211d}{a}");
  |                         ^ not found in this scope

error[[E0425]](https://doc.rust-lang.org/stable/error-index.html#E0425): cannot find value `a` in this scope
 --> src/main.rs:4:27
  |
4 |     format!("\u{1f4a3}{a}");
  |                           ^ not found in this scope

This reduces the number of skips to account for that

Fixes rust-lang/rust-clippy#9727

[rustbot]

r? @wesleywiser

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[wesleywiser]

lgtm but let's do a perf run just to make sure there's no impact

[wesleywiser]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit f5e390e with merge 1904eda6ee665febddb42ef6678305eb2472b264...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1904eda6ee665febddb42ef6678305eb2472b264 (1904eda6ee665febddb42ef6678305eb2472b264)

[rust-timer]

Queued 1904eda6ee665febddb42ef6678305eb2472b264 with parent a9ef100, future comparison URL.

[rust-timer]

Finished benchmarking commit (1904eda6ee665febddb42ef6678305eb2472b264): comparison URL.

Overall result: no relevant changes - 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-review -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

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

Cycles

Results

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.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Footnotes

1. the arithmetic mean of the percent change ↩

2. number of relevant changes ↩

[wesleywiser]

Thanks @Alexendoo!

@bors r+ rollup

[bors]

📌 Commit f5e390e has been approved by wesleywiser

It is now in the queue for this repository.