Debugger: Split updateWatchData() paths

There are two cases that do not coincide in asynchronous
engines such as the QmlEngine: Inserting a new watch item,
and expanding the children of an existing item.

Change-Id: Ic98a5f1e89aca37146039a241de737c407606e83
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggertooltipmanager.cpp

@@ -1222,7 +1222,7 @@ static void slotTooltipOverrideRequested
             m_tooltips.push_back(tooltip);
             tooltip->setState(PendingUnshown);
             if (engine->canHandleToolTip(context)) {
-                engine->updateWatchData(context.iname);
+                engine->updateItem(context.iname);
             } else {
                 ToolTip::show(point, DebuggerToolTipManager::tr("Expression too complex"),
                               Internal::mainWindow());