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.)

common/cogl-primitives.c

@@ -45,14 +45,13 @@ void _cogl_path_fill_nodes    ();
 void _cogl_path_stroke_nodes  ();
 
 void
-cogl_rectangle (float x,
-                float y,
-                float width,
-                float height)
+cogl_rectangle (float x1,
+                float y1,
+                float x2,
+                float y2)
 {
-  cogl_rectangle_with_multitexture_coords (x, y,
-                                           x+width,
-                                           y+height,
+  cogl_rectangle_with_multitexture_coords (x1, y1,
+                                           x2, y2,
                                            NULL,
                                            0);
 }