Only fetch and display a given notification once (#3626)

When fetching:

- Maintain a marker with the position of the newest fetched notification
- Use the marker to determine which notifications to fetch
- Fetch notifications with min_id to ensure that none are lost
- Update the marker as necessary
- Perform a one-time immediate fetch of notifications on startup

When creating notifications:

- Identify each notification with tag=${MastodonNotificationId}, id=${account.id}
- Remove activeNotifications field, it's no longer necessary
- Use the tag/id tuple to reliably identify existing notifications and avoid creating duplicates
- Cancelling notifications for an account must iterate over all the notifications, and individually remove the notifications that exist for that account.
- Limit notifications to a maximum of 40 (excluding summary notifications)
- Remove notifications (oldest first) to get under this limit
- Rate limit notification creation to 1 per second, so the OS won't drop them

Adjust the summary notification:

- Ensure the summary notification and the child notifications have the same group key
- Dismiss the summary notification if there is only one child notification

NotificationClearBroadcastReceiver is no longer needed, so remove it, and the need for deletePendingIntent.

Fixes #3625, #3539

app/src/test/java/com/keylesspalace/tusky/MainActivityTest.kt

@@ -90,8 +90,9 @@ class MainActivityTest {
         NotificationHelper.createNotificationChannelsForAccount(accountEntity, context)
 
         runInBackground {
-            NotificationHelper.make(
+            val notification = NotificationHelper.make(
                 context,
+                notificationManager,
                 Notification(
                     type = type,
                     id = "id",
@@ -110,6 +111,7 @@ class MainActivityTest {
                 accountEntity,
                 true
             )
+            notificationManager.notify("id", 1, notification)
         }
 
         val notification = shadowNotificationManager.allNotifications.first()