Allow decoupling of display updates from the display link refresh rate for testing
radar://89051816
<rdar://problem/97834557>
Pull request: https://github.com/WebKit/WebKit/pull/2877
Committed 253091@main (2143d60f9928): <https://commits.webkit.org/253091@main> Reviewed commits have been landed. Closing PR #2877 and removing active labels.