Reset the whole Qt model when an entry in the EditorEntityModel is removed. (#48) (#82)

An optimization introduced in Prefab mode currently changes the relative ordering of children, causing stale QModelIndex variables to still be referenced and crash the Editor sporadically. This change is theoretically a bit slower, but still much faster than the pre-optimization times.

Co-authored-by: Shirang Jia <shiranj@amazon.com>

Co-authored-by: Shirang Jia <shiranj@amazon.com>

Code/Framework/AzToolsFramework/AzToolsFramework/UI/Outliner/EntityOutlinerListModel.cpp

@@ -1344,14 +1344,15 @@ namespace AzToolsFramework
         emit EnableSelectionUpdates(false);
         auto parentIndex = GetIndexFromEntity(parentId);
         auto childIndex = GetIndexFromEntity(childId);
-        beginRemoveRows(parentIndex, childIndex.row(), childIndex.row());
+        beginResetModel();
     }
 
     void EntityOutlinerListModel::OnEntityInfoUpdatedRemoveChildEnd(AZ::EntityId parentId, AZ::EntityId childId)
     {
         (void)childId;
         AZ_PROFILE_FUNCTION(AZ::Debug::ProfileCategory::AzToolsFramework);
-        endRemoveRows();
+
+        endResetModel();
 
         //must refresh partial lock/visibility of parents
         m_isFilterDirty = true;