[UI-side compositing] Fix ScrollerMac::scrollbarState
<rdar://problem/107384908>
Pull request: https://github.com/WebKit/WebKit/pull/12132
Committed 262303@main (ec1f7d407a9b): <https://commits.webkit.org/262303@main> Reviewed commits have been landed. Closing PR #12132 and removing active labels.