add directional focus navigation for floating windows

Map left/down to previous and right/up to next in the workspace
stacking order, with wrapping. Does not cross to the tiled layer.

src/ifs/wl_seat.rs

@@ -826,6 +826,38 @@ impl WlSeatGlobal {
                 && let Some(c) = p.node_into_container()
             {
                 c.move_focus_from_child(self, tl.deref(), direction);
+            } else if let Some(float) = data.float.get()
+            {
+                let ws = float.workspace.get();
+                let floats: Vec<_> = ws
+                    .stacked
+                    .iter()
+                    .filter_map(|node| (*node).clone().node_into_float())
+                    .filter(|f| f.child.get().is_some())
+                    .collect();
+                if let Some(pos) = floats.iter().position(|f| f.id == float.id) {
+                    let target = match direction {
+                        Direction::Left | Direction::Down => {
+                            if pos == 0 {
+                                floats.last()
+                            } else {
+                                floats.get(pos - 1)
+                            }
+                        }
+                        _ => {
+                            if pos + 1 >= floats.len() {
+                                floats.first()
+                            } else {
+                                floats.get(pos + 1)
+                            }
+                        }
+                    };
+                    if let Some(f) = target
+                        && f.id != float.id
+                    {
+                        f.clone().node_do_focus(self, Direction::Unspecified);
+                    }
+                }
             }
         }
         self.maybe_schedule_warp_mouse_to_focus();