Add a display_lossy() to write a JsString lossily

[hansl]

This is faster when we don't need to keep the unpaired surrogates.

[codecov]

Codecov Report

Attention: Patch coverage is 62.50000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 52.85%. Comparing base (6ddc2b4) to head (9e1e0c5).
Report is 275 commits behind head on main.

Files with missing lines	Patch %	Lines
core/string/src/lib.rs	0.00%	2 Missing ⚠️
core/string/src/display.rs	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4023      +/-   ##
==========================================
+ Coverage   47.24%   52.85%   +5.61%     
==========================================
  Files         476      482       +6     
  Lines       46892    46728     -164     
==========================================
+ Hits        22154    24699    +2545     
+ Misses      24738    22029    -2709     

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[jedel1043]

Looks perfect!