messageTray: Add object holding sound for a notification

A notification can have two ways to specify a sound, via a name of a
sound in the sound theme and/or a file. Therefore introduce an object
that can hold both properties and creates an abstraction over the
different source. This reduces the number of properties for a
notification, which will make it simpler to port it to GObject
properties.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3173>

js/ui/notificationDaemon.js

@@ -204,8 +204,7 @@ class FdoNotificationDaemon {
             gicon,
             bannerMarkup: true,
             clear: true,
-            soundFile,
-            soundName: hints['sound-name'],
+            sound: new MessageTray.Sound(soundFile, hints['sound-name']),
         });
 
         let hasDefaultAction = false;