Update RenderLayerBacking to store backingSharingLayers in a WeakListHashSet instead of a Vector. This is beneficial to performance as we keep doing linear searches in the vector otherwise.
Pull request: https://github.com/WebKit/WebKit/pull/17682
Committed 267912@main (3a63df505058): <https://commits.webkit.org/267912@main> Reviewed commits have been landed. Closing PR #17682 and removing active labels.
<rdar://problem/115378252>