[WebGPU] Unify Surface and SwapChain into a single class
<rdar://problem/104312969>
Pull request: https://github.com/WebKit/WebKit/pull/8708
Committed 258984@main (a5b1ddef1f3b): <https://commits.webkit.org/258984@main> Reviewed commits have been landed. Closing PR #8708 and removing active labels.