chat-view: add a larger offscreen buffer for the message list view

Message delegates can have different heights and scrolling through the list view may cause vertical flickering without a substantial pre-fetching of items.

GitLab: #1020
Change-Id: Ic776b67d62773294f4548be3475804cd1824ef2b

src/app/mainview/components/MessageListView.qml

 /*
  * Copyright (C) 2021-2023 Savoir-faire Linux Inc.
- * Author: Trevor Tabah <trevor.tabah@savoirfairelinux.com>
- * Author: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -169,6 +167,11 @@ JamiListView {
     topMargin: 12
     spacing: 2
 
+    // The offscreen buffer is set to a reasonable value to avoid flickering
+    // when scrolling up and down in a list with items of different heights.
+    displayMarginBeginning: 2048
+    displayMarginEnd: 2048
+
     maximumFlickVelocity: 2048
     verticalLayoutDirection: ListView.BottomToTop
     boundsBehavior: Flickable.StopAtBounds