* Take SUPPORT_FRACTIONAL_TRANSLATION into account when diffing layers
* Store cull_rect in device coordinates
This removes the need to update cull rect coordinates when overriding transform
and is also consistent with how Layer::needs_painting() works.
* Use original transform for culling, but overriden transform to get paint coordinates.
This is to replicate the paint process during diffing, where layers are culled first and only then after paint the matrix is overriden.
* Rewrite AddLayerBounds based on @flar's suggestions
