Use WeakHashSet<T> / ThreadSafeWeakHashSet<T> instead of HashSet<T*> more in WebCore, for extra safety.
Pull request: https://github.com/WebKit/WebKit/pull/17668
Committed 267914@main (6ec1bbcc639f): <https://commits.webkit.org/267914@main> Reviewed commits have been landed. Closing PR #17668 and removing active labels.
<rdar://problem/115379135>