Used by the routine at update_sprite_loop.

Called by the main loop at update_sprite_loop for every object before its handler runs: copies the current width, height and pixel position (+$18 to +$1B) to +$1C to +$1F. Whatever the handler then does, set_draw_objs_overlapped can compare the new rectangle with the one the object had at the start of the frame, and render_dynamic_objects knows which area to wipe.