wayland: Fix drag-and-drop in firefox
Firefox does not like that wl_data_offer.source_actions is sent after the wl_data_device.enter event.
Another issue is that kwin does not send wl_data_device.leave event after drop occurs and that seems to break some state tracking code in Firefox, so the first dnd may work, but the next ones won't.
Edited by Vlad Zahorodnii