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/settings/SettingsConstants.kt

@@ -41,7 +41,7 @@ enum class AppTheme(val value: String) {
  *
  * - Adding a new preference that does not change the interpretation of an existing preference
  */
-const val SCHEMA_VERSION = 2023022701
+const val SCHEMA_VERSION = 2023072401
 
 object PrefKeys {
     // Note: not all of these keys are actually used as SharedPreferences keys but we must give
@@ -61,7 +61,6 @@ object PrefKeys {
     const val ANIMATE_GIF_AVATARS = "animateGifAvatars"
     const val USE_BLURHASH = "useBlurhash"
     const val SHOW_SELF_USERNAME = "showSelfUsername"
-    const val SHOW_NOTIFICATIONS_FILTER = "showNotificationsFilter"
     const val SHOW_CARDS_IN_TIMELINES = "showCardsInTimelines"
     const val CONFIRM_REBLOGS = "confirmReblogs"
     const val CONFIRM_FAVOURITES = "confirmFavourites"
@@ -104,4 +103,9 @@ object PrefKeys {
 
     /** UI text scaling factor, stored as float, 100 = 100% = no scaling */
     const val UI_TEXT_SCALE_RATIO = "uiTextScaleRatio"
+
+    /** Keys that are no longer used (e.g., the preference has been removed */
+    object Deprecated {
+        const val SHOW_NOTIFICATIONS_FILTER = "showNotificationsFilter"
+    }
 }