Manipulator: new cage2d manipulator

Adding alongside the existing one for now,
but it should eventually replace it.

Uses a matrix instead of (position + scale),
written so rotation can be done more easily.

Currently has a primitive handle for rotation, supports corner scaling.

source/blender/editors/space_api/spacetypes.c

@@ -133,6 +133,7 @@ void ED_spacetypes_init(void)
 	ED_manipulatortypes_arrow_3d();
 	ED_manipulatortypes_primitive_3d();
 	ED_manipulatortypes_cage_2d();
+	ED_manipulatortypes_cage_2d_rotate();
 
 	/* register types for operators and manipulators */
 	spacetypes = BKE_spacetypes_list();