Cherrypick Hide local edit message to 23.04

When a local message is edited make sure that the initial message that will be merged remains hidden so it doesn't flash up then disappear.

closes network/neochat#314


(cherry picked from commit 4e16b91f54)

src/models/messageeventmodel.cpp

@@ -605,6 +605,11 @@ QVariant MessageEventModel::data(const QModelIndex &idx, int role) const
 
     if (role == SpecialMarksRole) {
         if (isPending) {
+            // A pending event with an m.new_content key will be merged into the
+            // original event so don't show.
+            if (evt.contentJson().contains("m.new_content")) {
+                return EventStatus::Hidden;
+            }
             return pendingIt->deliveryStatus();
         }