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/operator_modal_view3d.py

@@ -8,7 +8,7 @@ class ViewOperator(bpy.types.Operator):
     bl_idname = "view3d.modal_operator"
     bl_label = "Simple View Operator"
 
-    offset = FloatVectorProperty(
+    offset: FloatVectorProperty(
         name="Offset",
         size=3,
     )