xwayland: Keep source/Xvisit alive for longer
SeatInterface emits dragEnded when the drag is dropped. The target may want to interact with the data source after the drop happened, for example only fetching data after the drop and not during the drag. (Note that the Wayland protocol has the same Xvisits are now not deleted prematurely but only when they are really finished. (Note that the Wayland protocol has the same distinction between dropped and finished so it maps nicely). For storing previous visits the same code pattern as in the rest of the XWayland DND code is used. The SelectionSource is reset when the next Drag/Drop operation involving a X window is started (see startDrag and doHandleXfixesNotify) or when the Wayland source is about to be deleted.
BUG:450460 FIXED-in:5.25.0