notification: Define how apps can get an activation-token via ActionInvoked

We need to hand out the activation token for XDG Activation in some way.
I think it's pretty nice that we can just add the same platform data as
used for DBus Activation to the ActionInvoked signal.

Author: jsparber

data/org.freedesktop.impl.portal.Notification.xml

@@ -128,10 +128,14 @@
         @app_id: App id of the application
         @id: the application-provided ID for the notification
         @action: the name of the action
-        @parameter: array which will contain the target parameter for the action, if one was specified
+        @parameter: an array containing additional information
 
         Send to the application when a non-exported action is
         activated.
+
+        The @parameter contains the target parameter for the action, if one was specified,
+        and the `platform-data` as vardict containing an ``activation-token`` (``s``) for `XDG Activation
+        <https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/staging/xdg-activation/xdg-activation-v1.xml>`_.
     -->
     <signal name="ActionInvoked">
       <arg type="s" name="app_id"/>

data/org.freedesktop.portal.Notification.xml

@@ -40,7 +40,7 @@
       <https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s08.html>`_
       using ``ActivateAction()`` method in the
       ``org.freedesktop.Application`` interface. An `activation-token` for
-      ` XDG Activation
+      `XDG Activation
       <https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/staging/xdg-activation/xdg-activation-v1.xml>`_
       and an application-defined `target` is passed when activating the action.
       Other
@@ -428,10 +428,14 @@
         ActionInvoked:
         @id: the application-provided ID for the notification
         @action: the name of the action
-        @parameter: array which will contain the target parameter for the action, if one was specified
+        @parameter: an array containing additional information
 
         Send to the application when a non-exported action is
         activated.
+
+        The @parameter contains the target parameter for the action, if one was specified,
+        and the `platform-data` as vardict containing an ``activation-token`` (``s``) for `XDG Activation
+        <https://gitlab.freedesktop.org/wayland/wayland-protocols/-/blob/main/staging/xdg-activation/xdg-activation-v1.xml>`_.
     -->
     <signal name="ActionInvoked">
       <arg type="s" name="id"/>