Move the notion of `delegatesScrolling` from WebPageProxy to DrawingAreaProxy, since this is presentation-related. This was only actually used in RemoteLayerTreeDrawingAreaProxy to control the indicator position, but future patches will make more use of it. Also have the DrawingAreaProxy be the factory for the RemoteScrollingCoordinatorProxy.
<rdar://problem/100924685>
Pull request: https://github.com/WebKit/WebKit/pull/5162
Committed 255356@main (263b327294f3): <https://commits.webkit.org/255356@main> Reviewed commits have been landed. Closing PR #5162 and removing active labels.