Use the WebCore type IntSize to store the framebuffer dimensions instead of separate width & height.
<rdar://problem/110377022>
Pull request: https://github.com/WebKit/WebKit/pull/14729
Committed 264966@main (2ef6856abf7b): <https://commits.webkit.org/264966@main> Reviewed commits have been landed. Closing PR #14729 and removing active labels.