qmllint: warn about duplicate names

qmllint does not warn about duplicate names in signals/properties/...

For example, it does not warn about following code:

import QtQuick

Item {
    property int helloWorld
    signal helloWorld
    function helloWorld() {}
    Item { id: helloWorld }
}

but it should warn that helloWorld cannot be a function, a signal, a property or an id at the same time.