Remove dependency on SimonCropp/Polyfill

[bkoelman]

Replace the dependency on SimonCropp/Polyfill (used by source generators) by inlining only the bits we need.

This prevents Dependabot notifications (usually multiple per week) each time a new version of the dependency is published.

QUALITY CHECKLIST

• Changes implemented in code
• Complies with our contributing guidelines
• N/A: Adapted tests
• N/A: Documentation updated

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.01%. Comparing base (cc3e1b6) to head (380d76a).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2075   +/-   ##
=======================================
  Coverage   92.01%   92.01%           
=======================================
  Files         364      364           
  Lines       11879    11879           
  Branches     1991     1991           
=======================================
  Hits        10930    10930           
  Misses        586      586           
  Partials      363      363           

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