lib: gbk decoder is gb18030 decoder per spec

[ChALkeR]

Tracking: #61041

Spec ref: https://encoding.spec.whatwg.org/#gbk-decoder

Without this, TextDecoder fails tests on gbk encoding

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.52%. Comparing base (4f24aff) to head (cf150ec).
⚠️ Report is 45 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61099      +/-   ##
==========================================
- Coverage   88.53%   88.52%   -0.02%     
==========================================
  Files         703      703              
  Lines      208546   208548       +2     
  Branches    40217    40213       -4     
==========================================
- Hits       184634   184607      -27     
- Misses      15926    15961      +35     
+ Partials     7986     7980       -6     

Files with missing lines	Coverage Δ
lib/internal/encoding.js	99.51% <100.00%> (+<0.01%)	⬆️

... and 37 files with indirect coverage changes

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[mertcanaltin]

LGTM

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/70587/