src: use simdutf for two-byte string utf8 conversion in utf8 value

[mertcanaltin]

latin-1 already used simdutf #61696,

I changed WriteUtf8V2 to simdutf for two-byte strings.

➜  node git:(mert/use-simdutf-for-two-byte-utf8) ✗ node-benchmark-compare ./result.csv
                                                confidence improvement accuracy (*)   (**)  (***)
util/utf8-value.js n=5000000 type='ascii'                      -0.11 %       ±2.64% ±3.69% ±5.18%
util/utf8-value.js n=5000000 type='mixed'              ***     49.60 %       ±1.90% ±2.67% ±3.78%
util/utf8-value.js n=5000000 type='three_bytes'        ***     31.10 %       ±2.42% ±3.34% ±4.60%
util/utf8-value.js n=5000000 type='two_bytes'          ***     42.75 %       ±1.42% ±1.94% ±2.66%

Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 4 comparisons, you can thus expect the following amount of false-positive results:
  0.20 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.04 false positives, when considering a   1% risk acceptance (**, ***),
  0.00 false positives, when considering a 0.1% risk acceptance (***)

[nodejs-github-bot]

Review requested:

• @nodejs/performance

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.68%. Comparing base (da5843b) to head (fb16b2d).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
src/util.cc	90.90%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #62248   +/-   ##
=======================================
  Coverage   89.67%   89.68%           
=======================================
  Files         676      676           
  Lines      206469   206507   +38     
  Branches    39537    39538    +1     
=======================================
+ Hits       185157   185199   +42     
+ Misses      13448    13447    -1     
+ Partials     7864     7861    -3     

Files with missing lines	Coverage Δ
src/util.cc	87.41% <90.90%> (-0.03%)	⬇️

... and 35 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.

[lemire]

Possibly, this could be utf16_to_utf8? I would test this on a big endian system to be sure.

[mertcanaltin]

thanks for review, I changed to convert_utf16_to_utf8 which uses platform-native endianness, and updated bench result