Use UniqueRef<> for TreeScope::m_idTargetObserverRegistry as it can never be null.
Pull request: https://github.com/WebKit/WebKit/pull/11568
Committed 261719@main (ff362c437909): <https://commits.webkit.org/261719@main> Reviewed commits have been landed. Closing PR #11568 and removing active labels.
<rdar://problem/106778960>