requestScrollPositionUpdate() and requestAnimatedScrollToPosition() do pretty much the same thing; we can just pass a ScrollIsAnimated argument and share more code.
<rdar://problem/109386012>
Pull request: https://github.com/WebKit/WebKit/pull/13908
Committed 264119@main (4a8d697cd1a2): <https://commits.webkit.org/264119@main> Reviewed commits have been landed. Closing PR #13908 and removing active labels.