Object Mode: move logic to 'object_modes.c'

Was mixed with edit-mode, centralize mode switching in a single file.

No functional changes.

source/blender/editors/object/CMakeLists.txt

@@ -50,6 +50,7 @@ set(SRC
 	object_hook.c
 	object_lattice.c
 	object_lod.c
+	object_modes.c
 	object_modifier.c
 	object_ops.c
 	object_random.c