Assignments to QML enumeration properties get autocompleted with string values

https://doc.qt.io/qt-5/qml-enumeration.html For backwards compatibility, the enumeration value may also be specified as a string, e.g. "AlignRight". This form is not recommended for new code.

Currently QtCreator autocompletes enumeration values to string values. (e.g. when pressing Ctrl+Space, see attached image qt_creator_auto_complete_enumeration.png)

If string values are not recommended for new code, we should not suggest/autocomplete them.