visionOS: backdrop-filter in a transparent web view on top of material background renders black
<rdar://problem/112798317>
Pull request: https://github.com/WebKit/WebKit/pull/17660
Committed 267875@main (780a84bad82a): <https://commits.webkit.org/267875@main> Reviewed commits have been landed. Closing PR #17660 and removing active labels.