fix(regexp): escape leading digit

[kt3k]

This PR updates escape of @std/regexp. Now escape escapes the leading digit as recommended in #3656. This behavior is aligned with regexp-escape proposal ( https://github.com/tc39/proposal-regex-escaping, polyfill: https://npm.im/regexp.escape )

closes #3656

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.53%. Comparing base (4989ba7) to head (7a8b7c2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6208   +/-   ##
=======================================
  Coverage   96.52%   96.53%           
=======================================
  Files         533      533           
  Lines       40871    40872    +1     
  Branches     6120     6120           
=======================================
+ Hits        39451    39456    +5     
+ Misses       1378     1374    -4     
  Partials       42       42           

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