Display notification filter/clear actions as menu items (#3877)

Previously the notification filter and clear actions were shown as
buttons in the UI, with a preference that determined whether they were
displayed.

Remove this preference, and display them as menu items.

- "Filter notifications" is shown as an icon, if possible
- "Clear notifications" is only ever shown as a menu item, to reduce the
chance the user inadvertently selects it

To ensure that the options menu appears correctly, remove the code that
creates a "fake" action bar, and adjust the layouts so that there are
three toolbars;

- mainToolbar -- displays the icons, and the current "location" (Home,
Notifications, etc)
- topNav -- displays the row of tabs at the top
- bottomNav -- displays the row of tabs at the bottom

Only one of them is set as the support action bar (depending on the
user's preferences). This provides the "show a logo" and "show the
options menu" functionality as standard, without needing to re-implement
as the previous code did.

app/src/main/java/com/keylesspalace/tusky/TuskyApplication.kt

@@ -130,6 +130,12 @@ class TuskyApplication : Application(), HasAndroidInjector {
             editor.remove(PrefKeys.MEDIA_PREVIEW_ENABLED)
         }
 
+        if (oldVersion < 2023072401) {
+            // The notifications filter / clear options are shown on a menu, not a separate bar,
+            // the preference to display them is not needed.
+            editor.remove(PrefKeys.Deprecated.SHOW_NOTIFICATIONS_FILTER)
+        }
+
         editor.putInt(PrefKeys.SCHEMA_VERSION, newVersion)
         editor.apply()
     }