merge_pr_52886

Fix and test resizeobserver interaction with CSS zoom.

The device pixel border-box size shouldn't be unzoomed.

Differential Revision: https://phabricator.services.mozilla.com/D251858

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1967762
gecko-commit: 2b0ec7bfaee2873076b8338deb816502c4ef9aa7
gecko-reviewers: jfkthame, layout-reviewers, dshin