overriding `padding` property of a inherited layout doesn't work.

[ogoffart]

The padding: 16px has no effect unless there is also a padding on the component

component TopBar inherits VerticalLayout {
    // padding: 0;  // uncommenting this line make it work
    height: 56px;
    Rectangle {
        background: red;
        
    }
}

export component MainWindow inherits Window {
    preferred-height: 380px;
    preferred-width: 230px;
    background: blue;
    VerticalLayout {
        TopBar {
            padding: 16px;
        }

        Rectangle {
            background: black;
        }
    }
}

Discussed in #8061