constructing font atlas without factoring in StackingContexts is broken

[Gankra]

We need to factor in scale transforms when constructing the font atlas, or else we get a blurry mess (with subpixel aa!)

Webrender:

Chrome:

(ignore that chrome messed up the shadow here)

[Gankra]

In particular this means parallel glyph processing on the backend is mostly busted. A possible fix would be to have PushText consult the parent stacking context(s?)'s transforms to compute this for the backend?

[glennw]

This depends on #1542.

[glennw]

@lsalzman @gankro I think this can be closed now?

[lsalzman]

Yes, this is fixed.