classic: Add missing top bar indicators

The only intended difference from the regular session is that the
date menu moves to the right. However in the meantime, gnome-shell
added a couple more (usually hidden) indicators, but we never
updated the session mode definition.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/339>
(cherry picked from commit 81aade6659)

data/classic.json.in

@@ -5,6 +5,6 @@
     "enabledExtensions": [@CLASSIC_EXTENSIONS@],
     "panel": { "left": ["activities"],
                "center": [],
-               "right": ["a11y", "keyboard", "dateMenu", "quickSettings"]
+               "right": ["screenRecording", "screenSharing", "dwellClick", "a11y", "keyboard", "dateMenu", "quickSettings"]
              }
 }