Add ability to change popup in PortableColorPicker

[CPKreu]

Basically so that you can do something like this

<PortableColorPicker>
    <PortableColorPicker.ColorPicker>
        <StackPanel>
            <StandardColorPicker />
            <Button>idk</Button>
        </StackPanel>
    </PortableColorPicker.ColorPicker>
</PortableColorPicker>

[Equbuxu]

I'm not doing this in 3.0.0

[flabbet]

It is possible in AvaloniaUI version if you create your own control template