For UI-side scroller hit-testing we need ScrollingNodeIDs on RemoteLayerTreeNodes, so plumb them through via PlatformCALayerRemote.
<rdar://problem/102499187>
Pull request: https://github.com/WebKit/WebKit/pull/6621
Committed 256842@main (4b08e3ef1c8a): <https://commits.webkit.org/256842@main> Reviewed commits have been landed. Closing PR #6621 and removing active labels.