…h the primitive in WR r=gw

Instead of trying to extract an inner rectangle from a transformed inner rectange,
which by itself doesn't have an obviously "best" solution, we are going to test if the
visibility rect is within the polygon of the projected inner rect.

The test is more precise, could be slightly more heavy, but most importantly - it's correct.

Differential Revision: https://phabricator.services.mozilla.com/D65836

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/1692426a9549efd97f3241b8fc314eac0786a750