feat(core): add unicode_string_view and js_value_wrapper

[churchill-zhang]

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• Test cases have been added/updated for the code you will submit.
• Documentation has added or updated.
• Commit message is following the Convention Commit guideline.
• Squash the repeat code commits, short patches are welcome.

[codecov-commenter]

Codecov Report

Merging #782 (d586854) into master (8d75ed0) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #782   +/-   ##
=======================================
  Coverage   60.05%   60.05%           
=======================================
  Files          26       26           
  Lines        1675     1675           
=======================================
  Hits         1006     1006           
  Misses        669      669           

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[ilikethese]

TL;DR;