QmlDesigner: Add emit for isBoundChanged if expression is set

The value in some cases is not changing and therefore the icon
based on isBound was not updated.

Change-Id: I6b0ed8df6e0f5854660e54b4753a4c15107cda66
Reviewed-by: Ali Kianian <ali.kianian@qt.io>
(cherry picked from commit f8e71efc5a)
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/qmldesigner/components/propertyeditor/propertyeditorvalue.cpp

@@ -160,6 +160,7 @@ void PropertyEditorValue::setExpressionWithEmit(const QString &expression)
         emit expressionChanged(nameAsQString());
         emit expressionChangedQml();// Note that we set the name in this case
     }
+    emit isBoundChanged();
 }
 
 void PropertyEditorValue::setExpression(const QString &expression)