Use all-scroll instead of fleur xcursor shape for window dragging

When there are no xcursor themes available, Wayland uses its own built-in shapes [1].
Wayland (and thus to extend wlroots) is based on the XDG's cursor spec [2],
which itself is based on CSS' [3][4], neither of which define `fleur` shape. So dwl,
without any external themes, falls back to `default` shape when dragging a window.
There is `all-scroll` shape that is being symlinked to (or vice versa) by `move`,
`dnd-move`, `grabbed` and `fleur` shapes by various themes.

Since `all-scroll` is being symlinked to anyway, and has been part of all relevant
specs as the shape for this use case for a very long time now, use it instead.

[1] https://gitlab.freedesktop.org/wayland/wayland/-/blob/main/cursor/cursor-data.h#L559
[2] https://www.freedesktop.org/wiki/Specifications/cursor-spec
[3] https://drafts.csswg.org/css-ui/#cursor
[4] https://developer.mozilla.org/en-US/docs/Web/CSS/cursor

dwl.c

@@ -1965,7 +1965,7 @@ moveresize(const Arg *arg)
 	case CurMove:
 		grabcx = (int)round(cursor->x) - grabc->geom.x;
 		grabcy = (int)round(cursor->y) - grabc->geom.y;
-		wlr_cursor_set_xcursor(cursor, cursor_mgr, "fleur");
+		wlr_cursor_set_xcursor(cursor, cursor_mgr, "all-scroll");
 		break;
 	case CurResize:
 		/* Doesn't work for X11 output - the next absolute motion event