fs: dispatch ASCII and Latin1 via simdutf in ReadFileUtf8

[mertcanaltin]

In fs.readFileSync(path, 'utf8'), I dispatch the V8 string creation through simdutf. ASCII and Latin1-fits utf-8 use one-byte V8 strings, multibyte goes through simdutf to UTF-16, invalid utf-8 falls back to V8.

@nodejs/fs, @anonrig @addaleax, @lemire @mcollina

Bench results (gist): https://gist.github.com/mertcanaltin/a0096c3fad387d0bace821938754af44

fs/readfile-utf8-fastpath.js
    latin1     path 4MB     +803%
    latin1     path 256KB   +725%
    utf8_mixed path 4MB     +453%
    utf8_mixed path 256KB   +358%
    latin1     path 16KB    +309%
    latin1     fd   4MB     +238%

[nodejs-github-bot]

Review requested:

• @nodejs/performance

[codecov]

Codecov Report

❌ Patch coverage is 67.92453% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.04%. Comparing base (9de9b9f) to head (cdeaa76).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/node_file.cc	67.92%	11 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #63370      +/-   ##
==========================================
- Coverage   90.07%   90.04%   -0.04%     
==========================================
  Files         714      714              
  Lines      225564   225613      +49     
  Branches    42656    42668      +12     
==========================================
- Hits       203177   203145      -32     
- Misses      14189    14254      +65     
- Partials     8198     8214      +16     

Files with missing lines	Coverage Δ
src/node_file.cc	74.15% <67.92%> (-0.08%)	⬇️

... and 54 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.