Python API: update animation example in quickstart docs for slots

Update the Animation example in the Python API: Quickstart documentation
to use slotted Actions.

Pull Request: https://projects.blender.org/blender/blender/pulls/140334

doc/python_api/rst/info_quickstart.rst

@@ -447,9 +447,22 @@ Using low-level functions:
 .. code-block:: python
 
    obj = bpy.context.object
-   obj.animation_data_create()
-   obj.animation_data.action = bpy.data.actions.new(name="MyAction")
-   fcu_z = obj.animation_data.action.fcurves.new(data_path="location", index=2)
+
+   # Create the action, with a slot for the object, a layer, and a keyframe strip:
+   action = bpy.data.actions.new(name="MyAction")
+   slot = action.slots.new(obj.id_type, obj.name)
+   strip = action.layers.new("MyLayer").strips.new(type='KEYFRAME')
+
+   # Create a channelbag to hold the F-Curves for the slot:
+   channelbag = strip.channelbag(slot, ensure=True)
+
+   # Create the F-Curve with two keyframes:
+   fcu_z = channelbag.fcurves.new(data_path="location", index=2)
    fcu_z.keyframe_points.add(2)
    fcu_z.keyframe_points[0].co = 10.0, 0.0
    fcu_z.keyframe_points[1].co = 20.0, 1.0
+
+   # Assign the action and the slot to the object:
+   adt = obj.animation_data_create()
+   adt.action = action
+   adt.action_slot = slot