Deploy WeakPtr and WeakHashMap in PlaybackSessionManager and VideoFullscreenManager.
Pull request: https://github.com/WebKit/WebKit/pull/10174
Committed 260382@main (b51fc8ba75c9): <https://commits.webkit.org/260382@main> Reviewed commits have been landed. Closing PR #10174 and removing active labels.
<rdar://problem/105555841>
Re-opened since this is blocked by bug 252423