[xwl] Notify wayland that our data offer is accepted
kwayland-server was updated to follow the result of whether the data offer was accepted before calling drop.
Our bridge was not updated.
We don't have enough data to know which mimeType the XWayland client actually has accepted, as that doesn't exist at an X11 level, but it doesn't have a big actual impact. Despite which mime type gets accepted any mimetype can be retrieved in the drop event.
Tested against "dropsite" from QtBase widget examples forced into xcb mode using dolphin as a source.