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 96.52%. Comparing base (4989ba7) to head (35f2606).
Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6208      +/-   ##
==========================================
- Coverage   96.52%   96.52%   -0.01%     
==========================================
  Files         533      534       +1     
  Lines       40871    40977     +106     
  Branches     6120     6134      +14     
==========================================
+ Hits        39451    39553     +102     
- Misses       1378     1382       +4     
  Partials       42       42              

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