Fix QML watch expressions for v8

Fix syncing of watch expressions with Qt Quick 2. For v8/v4 we're
utilizing the 'evaluate' command, which we have to re-send on every
change to get updates. We therefore now call synchronizeWatchers()
whenever the stack changes.

Task-number: QTCREATORBUG-13473
Change-Id: I7356e9518a719839c5cbb6e518be18e665078e85
Reviewed-by: Ulf Hermann <ulf.hermann@theqtcompany.com>
Reviewed-by: Robert Loehning <robert.loehning@theqtcompany.com>

src/plugins/debugger/qml/qmlengine.cpp

@@ -1176,6 +1176,8 @@ void QmlEngine::updateCurrentContext()
             context = grandParentData->name;
     }
 
+    synchronizeWatchers();
+
     QmlJS::ConsoleManagerInterface *consoleManager = qmlConsoleManager();
     if (consoleManager)
         consoleManager->setContext(tr("Context:") + QLatin1Char(' ') + context);