PyAPI: Use annotations for RNA definitions

- Logical use of fields since they define type information.
- Avoids using ordered-dict metaclass.

Properties using regular assignments will print a warning and load,
however the order is undefined.

release/scripts/templates_py/addon_add_object.py

@@ -45,7 +45,7 @@ class OBJECT_OT_add_object(Operator, AddObjectHelper):
     bl_label = "Add Mesh Object"
     bl_options = {'REGISTER', 'UNDO'}
 
-    scale = FloatVectorProperty(
+    scale: FloatVectorProperty(
         name="scale",
         default=(1.0, 1.0, 1.0),
         subtype='TRANSLATION',