Enable scroll anchoring by default
<rdar://problem/118365809>
Pull request: https://github.com/WebKit/WebKit/pull/20452
Committed 271283@main (8c670735053d): <https://commits.webkit.org/271283@main> Reviewed commits have been landed. Closing PR #20452 and removing active labels.
Re-opened since this is blocked by bug 265977
Pull request: https://github.com/WebKit/WebKit/pull/21537
Committed 271790@main (b19a8ecd83e6): <https://commits.webkit.org/271790@main> Reviewed commits have been landed. Closing PR #21537 and removing active labels.