Bug 1687573 - Add no-op shadow primitives directly to parent prim list. r=nical
Bug 1687573 - Add no-op shadow primitives directly to parent prim list. r=nical

This removes another code path that was creating pass through
picture primitives.

Differential Revision: https://phabricator.services.mozilla.com/D102359

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/6179ede2b9546cf6ff4a69d0d658457c6910f59a

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender