Update Set methods proposal

[zloirock]

• Set methods proposal:
  • Methods:
    • Set.prototype.intersection
    • Set.prototype.union
    • Set.prototype.difference
    • Set.prototype.symmetricDifference
    • Set.prototype.isSubsetOf
    • Set.prototype.isSupersetOf
    • Set.prototype.isDisjointFrom
  • Moved to Stage 3, November 2022 TC39 meeting
  • Reimplemented with new semantics:
    • Optimized performance (iteration over lowest set)
    • Accepted only Set-like objects as an argument, not all iterables
    • Accepted only Sets as this, no @@species support, and other minor changes
  • Added /actual/ entries, unconditional forced replacement changed to feature detection
  • For avoiding breaking changes:
    • New versions of methods are implemented as new modules and available in new entries or entries where old versions of methods were not available before (like /actual/ namespace)
    • In entries where they were available before (like /full/ namespace), those methods are available with fallbacks to old semantics (in addition to Set-like, they accept iterable objects). This behavior will be removed from the next major release

cc @bakkot