QmlDesigner: Fix workspace list update on clone

Adds a missing emit of workspaceListChanged when cloning a workspace in
the workspace manager. It will fix a missing update of the workspace
ComboBox in the toolbar.

Change-Id: Ic2eb3fe516841ba13456c7d94fe699518988ff7a
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/advanceddockingsystem/dockmanager.cpp

@@ -805,6 +805,7 @@ namespace ADS
             d->m_workspaces.insert(1, clone);
             d->m_workspaceDateTimes
                 .insert(clone, workspaceNameToFileName(clone).toFileInfo().lastModified());
+            emit workspaceListChanged();
             return true;
         }
         return false;