Allow containers to float

Things worth noting:

* When a fullscreen view unmaps, the check to unset fullscreen on the
workspace has been moved out of view_unmap and into container_destroy,
because containers can be fullscreen too
* The calls to `container_reap_empty_recursive(workspace)` have been
removed from `container_set_floating`. That function reaps upwards so it
wouldn't do anything. I'm probably the one who originally added it...
* My fix (b14bd1b0b1) for the tabbed child
crash has a side effect where when you close a floating container, focus
is not given to the tiled container again. I've removed my fix and
removed the call to `send_cursor_motion` from `seat_set_focus_warp`. We
should consider calling it from somewhere earlier in the call stack.

sway/desktop/render.c

@@ -779,7 +779,7 @@ static void render_floating_container(struct sway_output *soutput,
 		}
 		render_view(soutput, damage, con, colors);
 	} else {
-		render_container(soutput, damage, con, false);
+		render_container(soutput, damage, con, con->current.focused);
 	}
 }