Every RemoteImageBufferProxy gets a SharedVideoFrameWriter, but only very few use it, and it has creation/destruction cost because it owns an IPC::Semaphore.
<rdar://problem/111133625>
Pull request: https://github.com/WebKit/WebKit/pull/15170
Committed 265427@main (e97b0792a67c): <https://commits.webkit.org/265427@main> Reviewed commits have been landed. Closing PR #15170 and removing active labels.