Implement the Kitty Drag-and-Drop Protocol (OSC 72)

Kovid strikes again with yet another new protocol: https://sw.kovidgoyal.net/kitty/dnd-protocol/

The protocol is not yet stable, but I figure we can start writing a parser and then work on integrating it with the apprt. As with OSC 5522, some kind of state machine would be needed to concatenate all the received packets together for large payload streams.