Implement corner clipping.
Remove PixelFormat from WebrenderImageInfo.
Use WebRender text shadow.
Remove MallocSizeOf and Deserialize for DL items.
Closes#19649, #19680, #19802
This uses floating-point (Layout) coordinates in where possible.
Replace NormalBorder struct with WebRender equivalent.
Remove ToPointF and ToRectF traits.
Convert border RepeatKeyword with ToLayout.
Add some definitions to malloc_size_of for WebRender types.
This will allow Servo to create ClipScrollNodes later during display
list construction, which will be necessary once rounded rectangles
are removed from the LocalClip structure. Instead of keeping track
of the ClipId of each ClipScrollNode, we keep track of its index in an
array of ClipScrollNodes. This will allow us to access them without a
hash lookup.
