Bug 1707798 - Use rough clipping in cs_clip_image. r=aosmond
Bug 1707798 - Use rough clipping in cs_clip_image. r=aosmond

We were already clipping off most of the AA inside cs_clip_image previously anyway.
Given that it is too unpredictable in what situations the little bit of remaining
AA was actually applying, and that it causes visual artifacts sometimes when it
activates where it shouldn't, we're better off just using a rough clip inside this
shader for everything so that it is always predictable.

Differential Revision: https://phabricator.services.mozilla.com/D113545

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/02dbc4ee200d3b5e4746663cef76f09c55dfcbb3

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