Upstream `defaultAlternateFormControlDesignEnabled` and `defaultVideoFullscreenRequiresElementFullscreen`
<rdar://problem/110544922>
Pull request: https://github.com/WebKit/WebKit/pull/14823
Committed 265038@main (c976622eda34): <https://commits.webkit.org/265038@main> Reviewed commits have been landed. Closing PR #14823 and removing active labels.