Improve filenames encoding and misc

[Urgau]

This PR is a follow-up to #149709, it aims at preventing a double encoding when there are no remapping, as well as making some small improvements to the code.

Best reviewed commit by commit.

r? @davidtwco

[Urgau]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 986b8a6 (986b8a6ced00431c061e4320e4f6015fb61e8c94, parent: 08de25c4ea16d7ecc3ceeb093d4f343a2be30df5)

[rust-timer]

Finished benchmarking commit (986b8a6): comparison URL.

Overall result: ✅ improvements - 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

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

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

Max RSS (memory usage)

Results (secondary -3.3%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-3.5%, -3.1%]	2
All ❌✅ (primary)	-	-	0

Cycles

Results (primary 2.8%, secondary -3.0%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[2.8%, 2.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.0%	[-3.0%, -3.0%]	1
All ❌✅ (primary)	2.8%	[2.8%, 2.8%]	1

Binary size

Results (primary -0.1%, secondary -0.1%)

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)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	68
Improvements ✅ (secondary)	-0.1%	[-0.3%, -0.0%]	45
All ❌✅ (primary)	-0.1%	[-0.2%, -0.0%]	68

Bootstrap: 476.492s -> 478.982s (0.52%)
Artifact size: 390.29 MiB -> 390.28 MiB (-0.00%)