Add union, intersection and symmetric difference operations to HashSet to allow users to utilize idiomatic set functionality."
<rdar://problem/103074259>
Pull request: https://github.com/WebKit/WebKit/pull/7263
Committed 257569@main (5e4251036391): <https://commits.webkit.org/257569@main> Reviewed commits have been landed. Closing PR #7263 and removing active labels.