src: improve StringBytes::Encode perf on UTF8

[ChALkeR]

Tracking: #61041

Most data is valid utf-8, no need to wait for v8 optimizations or for simdutf implementing fast replacement.
We can just check + simdutf in fast case.

This is a 2x-10x speedup according to https://github.com/lemire/jstextdecoderbench bench (+ I added extra cases)

There is still room for improvement here (e.g. avoiding triple scans), but this change alone improves results significantly
We can improve further iteratively
This performs mallocs only for valid strings, instead of optimistically malloc-ing and decoding until error
Switching that behavior to optimistic would be a separate PR (perf needs to be checked against this not main or #61119)

Buffer#toString() - utf8

pre-#61119:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	18.21 GiB/s	0.005 ms
Arabic lipsum	79.771 KiB	0.29 GiB/s	0.266 ms
Chinese lipsum	68.203 KiB	0.34 GiB/s	0.192 ms
Arabic + 2 * ASCII	249.575 KiB	0.73 GiB/s	0.329 ms

main with #61119 (landed):

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.75 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	0.28 GiB/s	0.273 ms
Chinese lipsum	68.203 KiB	0.33 GiB/s	0.197 ms
Arabic + 2 * ASCII	249.575 KiB	0.69 GiB/s	0.344 ms

PR:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.84 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	2.03 GiB/s	0.038 ms
Chinese lipsum	68.203 KiB	4.06 GiB/s	0.016 ms
Arabic + 2 * ASCII	249.577 KiB	3.42 GiB/s	0.072 ms

TextDecoder, loose

pre-#61119:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	17.99 GiB/s	0.005 ms
Arabic lipsum	79.771 KiB	0.28 GiB/s	0.270 ms
Chinese lipsum	68.203 KiB	0.34 GiB/s	0.194 ms
Arabic + 2 * ASCII	249.577 KiB	0.71 GiB/s	0.333 ms

main with #61119 (landed):

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.59 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	0.28 GiB/s	0.271 ms
Chinese lipsum	68.203 KiB	0.34 GiB/s	0.192 ms
Arabic + 2 * ASCII	249.577 KiB	0.70 GiB/s	0.340 ms

PR:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.78 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	2.03 GiB/s	0.038 ms
Chinese lipsum	68.203 KiB	4.01 GiB/s	0.016 ms
Arabic + 2 * ASCII	249.577 KiB	3.42 GiB/s	0.072 ms

TextDecoder, fatal

pre-#61119:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	15.31 GiB/s	0.006 ms
Arabic lipsum	79.771 KiB	0.27 GiB/s	0.279 ms
Chinese lipsum	68.203 KiB	0.34 GiB/s	0.194 ms
Arabic + 2 * ASCII	249.577 KiB	0.71 GiB/s	0.338 ms

main with #61119 (landed):

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.63 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	0.28 GiB/s	0.272 ms
Chinese lipsum	68.203 KiB	0.33 GiB/s	0.197 ms
Arabic + 2 * ASCII	249.577 KiB	0.68 GiB/s	0.351 ms

PR:

Test	Size	Throughput	Mean Time
Latin lipsum (ASCII)	84.902 KiB	36.71 GiB/s	0.002 ms
Arabic lipsum	79.771 KiB	1.70 GiB/s	0.046 ms
Chinese lipsum	68.203 KiB	2.97 GiB/s	0.022 ms
Arabic + 2 * ASCII	249.577 KiB	3.01 GiB/s	0.082 ms

---

cc @nodejs/performance

[ChALkeR]

As #61119 landed, this is now ready. Rebased.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.52%. Comparing base (955d347) to head (d4f0460).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/string_bytes.cc	50.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61131      +/-   ##
==========================================
- Coverage   88.52%   88.52%   -0.01%     
==========================================
  Files         704      704              
  Lines      208802   208895      +93     
  Branches    40318    40334      +16     
==========================================
+ Hits       184842   184924      +82     
+ Misses      15947    15940       -7     
- Partials     8013     8031      +18     

Files with missing lines	Coverage Δ
src/encoding_binding.cc	52.73% <ø> (ø)
src/string_bytes.cc	69.01% <50.00%> (-0.73%)	⬇️

... and 45 files with indirect coverage changes

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