scene: Expand surface damage if the surface is scaled

If the surface item's contents is scaled, i.e. its scale factor doesn't
match the output's scale, GL_LINEAR will be applied to smooth the
contents. The unfortunate thing is that it's possible some of the
changed pixels will bleed to the neighbor ones.

In order to handle that scenario better, this change makes the
SurfaceItem expand the damage if there's scale factor mismatch.

bufferSourceBox and bufferTransform properties were introduced to detect
if the surface contents is going to be scaled. bufferSourceBox covers
both crop transform from wp_viewport and scale factor from wl_surface.
bufferTransform is same as wl_surface's buffer transform property.