node-api: use WriteV2 in napi_get_value_string_utf16

[tniessen]

Since String::Write() is deprecated, use String::Write2() instead. That requires us to compute the correct number of characters ahead of time but removes the need for dealing with the return value.

[nodejs-github-bot]

Review requested:

• [ ] @nodejs/node-api

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 90.23%. Comparing base (6de55f7) to head (da6a60e). Report is 306 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #58165      +/-   ##
==========================================
+ Coverage   90.17%   90.23%   +0.05%     
==========================================
  Files         630      633       +3     
  Lines      186503   186807     +304     
  Branches    36614    36665      +51     
==========================================
+ Hits       168187   168565     +378     
+ Misses      11124    11041      -83     
- Partials     7192     7201       +9     

Files with missing lines	Coverage Δ
src/js_native_api_v8.cc	76.55% <100.00%> (+0.02%)	:arrow_up:

... and 86 files with indirect coverage changes

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[vmoroz]

Could you also replace the other deprecated Write functions in this file - the WriteOneByte and WriteUtf8?

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/66810/

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/66835/

[nodejs-github-bot]

Landed in 971148c39a0eadaa3b4e2395d2574dee68648875

[aduh95]

Adding https://github.com/nodejs/node/labels/dont-land-on-v22%2Ex as it looks like WriteV2 is not available on 22.x.