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/test/java/com/keylesspalace/tusky/components/notifications/NotificationsViewModelTestBase.kt

@@ -99,7 +99,6 @@ abstract class NotificationsViewModelTestBase {
             PrefKeys.CONFIRM_REBLOGS to true,
             PrefKeys.CONFIRM_FAVOURITES to false,
             PrefKeys.WELLBEING_HIDE_STATS_POSTS to false,
-            PrefKeys.SHOW_NOTIFICATIONS_FILTER to true,
             PrefKeys.FAB_HIDE to false
         )
 

app/src/test/java/com/keylesspalace/tusky/components/notifications/NotificationsViewModelTestUiState.kt

@@ -35,7 +35,6 @@ class NotificationsViewModelTestUiState : NotificationsViewModelTestBase() {
 
     private val initialUiState = UiState(
         activeFilter = setOf(Notification.Type.FOLLOW),
-        showFilterOptions = true,
         showFabWhileScrolling = true
     )
 
@@ -64,23 +63,4 @@ class NotificationsViewModelTestUiState : NotificationsViewModelTestBase() {
             assertThat(expectMostRecentItem().showFabWhileScrolling).isFalse()
         }
     }
-
-    @Test
-    fun `showFilterOptions depends on SHOW_NOTIFICATIONS_FILTER preference`() = runTest {
-        // Prior
-        viewModel.uiState.test {
-            assertThat(expectMostRecentItem().showFilterOptions).isTrue()
-        }
-
-        // Given
-        sharedPreferencesMap[PrefKeys.SHOW_NOTIFICATIONS_FILTER] = false
-
-        // When
-        eventHub.dispatch(PreferenceChangedEvent(PrefKeys.SHOW_NOTIFICATIONS_FILTER))
-
-        // Then
-        viewModel.uiState.test {
-            assertThat(expectMostRecentItem().showFilterOptions).isFalse()
-        }
-    }
 }