[Places Panel] Support drag and drop from Ark
Accepts Ark's special dnd mime types so that archive contents can be dragged onto a place to extract and/or (mount and) switch to the hovered location.
I can now drag a file from Ark ontop of a place in Dolphin, have it switch view to that location and drop the file ontop of a place to extract.
Extraction handling is implemented in Dolphin's DropHandler already but the view didn't accept the drop before.
I chose to implement it in Dolphin rather than KIO (even though that could enable drag-hover for archives in the file dialogs, too), since that would require more coupling of KFilePlacesModel and KFilePlacesView – the former of which should then accept the Ark type if dropOnPlace is on – as well as making assumption about apps from Frameworks code. I think this is good enough.