Remove the need to provide the registry to RenderStyle::customPropertyValue()
<rdar://problem/104953759>
Pull request: https://github.com/WebKit/WebKit/pull/9508
Committed 259807@main (ffe6d89e6fa5): <https://commits.webkit.org/259807@main> Reviewed commits have been landed. Closing PR #9508 and removing active labels.