Clean up various issues with ScrollerPairMac, fixing an RTL bug in the process.
<rdar://problem/106682101>
Pull request: https://github.com/WebKit/WebKit/pull/11479
Committed 261673@main (478618b3a4aa): <https://commits.webkit.org/261673@main> Reviewed commits have been landed. Closing PR #11479 and removing active labels.