shaped-texture: Account for linear sampling when calculating actor damage

Linear sampling can influence the value of surrounding pixels beyond the scaled framebuffer extents calculated during stage view rendering, resulting in flickering graphical artifacts due to unaccounted pixel changes. This is exhibited in xfreerdp and wlfreerdp at 150% display scaling.

Fix this by ensuring that all pixels that may be affected by linear scaling is included in the framebuffer redraw clip by padding the actor redraw clip.