Make WTF::Identified work with strongly typed identifiers instead of uint64_t. Keep existing code that was using the legacy WTF::Identified working by having it subclass WTF::LegacyIdentified instead. We should eventually port those to the new WTF::Identified. Also adopt WTF::Identified more broadly to reduce boilerplate code in the code base.
Pull request: https://github.com/WebKit/WebKit/pull/25523
Committed 275739@main (1b1dcd66b5d6): <https://commits.webkit.org/275739@main> Reviewed commits have been landed. Closing PR #25523 and removing active labels.
<rdar://problem/124142636>