Add a way to create JsString from single ASCII literal without heap allocation

[CrazyboyQCD]

Use js_string macro to create JsString from an ASCII literal currently causes heap allocation except for the StaticJsStrings, and StaticJsStrings is hard for compiler to do constant evaluation because of the HashMap.

Godbolt Link.
This adds a way to create JsString from ASCII literal without heap allocation and it is easy for compiler to evaluate constantly, you could view the asm result in the link.

[codecov]

Codecov Report

Attention: Patch coverage is 89.65517% with 3 lines in your changes missing coverage. Please review.

Project coverage is 50.90%. Comparing base (6ddc2b4) to head (a12fc23).
Report is 215 commits behind head on main.

Files	Patch %	Lines
core/string/src/lib.rs	89.65%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3927      +/-   ##
==========================================
+ Coverage   47.24%   50.90%   +3.65%     
==========================================
  Files         476      467       -9     
  Lines       46892    44643    -2249     
==========================================
+ Hits        22154    22725     +571     
+ Misses      24738    21918    -2820     

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