[WebGPU] Move prepareForDisplay() from PresentationContext to CompositorIntegration
<rdar://problem/104942364>
Pull request: https://github.com/WebKit/WebKit/pull/9498
Committed 259778@main (b54dc9debcec): <https://commits.webkit.org/259778@main> Reviewed commits have been landed. Closing PR #9498 and removing active labels.