feat(stdlib): add unicode/utf16 pacakge

[notJoon]

Description

• Add unicode/utf16 package. transffered directly from Go without any changes.
• register to the stdlibWhitelist transpiler.go

In an earlier JSON PR #1415 , I included this unicode/utf16 to handle unescaping and other byte slice operations, but realized that I wasn't using it in that package, leading me to submit a separate PR sepcifically for this.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.79%. Comparing base (7596f42) to head (541cb24).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1764      +/-   ##
==========================================
- Coverage   44.79%   44.79%   -0.01%     
==========================================
  Files         459      459              
  Lines       67642    67642              
==========================================
- Hits        30300    30297       -3     
- Misses      34808    34809       +1     
- Partials     2534     2536       +2     

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[deelawn]

Looks good but I'd strongly recommend removing the export_test.gno file and changing the package to utf16_test in utf16_test.gno. This is for a couple of reasons:

• It makes the test file's "unicode/utf16" import meaningful
• It separates testing code from the package code, ensuring that we are testing the same API users are interacting with.

This will require the package prefix to be added to the tests, but that's fine. The only reason the go stdlib tests for this package don't have that is because they use the dot import, something gno does not support.

[notJoon]

Looks good but I'd strongly recommend removing the export_test.gno file and changing the package to utf16_test in utf16_test.gno. This is for a couple of reasons:

I thought it was customary to include export_test since it was in other packages, but I will modify this part. Thank you 👍

[zivkovicmilos]

Looks good 💯