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.