Changes cogl_rectangle to take x1, y1, x2, y2 args not x1, y1, width, height

Changes cogl_rectangle to take x1, y1, x2, y2 args not x1, y1, width, height

This makes it consistent with cogl_rectangle_with_{multi,}texture_coords.
Notably the reason cogl_rectangle_with_{multi,}texture_coords wasn't changed
instead is that the former approach lets you describe back facing rectangles.
(though technically you could pass negative width/height values to achieve
 this; it doesn't seem as neat.)