add toggle focus between floating and tiled layers

Adds focus_floats(), toggle_focus_float_tiled(), and their IPC
bindings so users can bind a key to swap focus between the floating
and tiled layers.

src/ifs/wl_seat.rs

@@ -1163,6 +1163,36 @@ impl WlSeatGlobal {
         );
     }
 
+    pub fn toggle_focus_float_tiled(self: &Rc<Self>) {
+        let current = self.keyboard_node.get();
+        match current.node_layer().layer() {
+            NodeLayer::Tiled | NodeLayer::Fullscreen => self.focus_floats(),
+            _ => self.focus_tiles(),
+        }
+        self.maybe_schedule_warp_mouse_to_focus();
+    }
+
+    pub fn focus_floats(self: &Rc<Self>) {
+        let current = self.keyboard_node.get();
+        if current.node_layer().layer() == NodeLayer::Stacked {
+            return;
+        }
+        let Some(output) = current.node_output() else {
+            return;
+        };
+        let Some(ws) = output.workspace.get() else {
+            return;
+        };
+        if let Some(child) = ws
+            .stacked
+            .rev_iter()
+            .filter_map(|node| (*node).clone().node_into_float())
+            .find_map(|float| float.child.get())
+        {
+            child.node_do_focus(self, Direction::Unspecified);
+        }
+    }
+
     pub fn focus_tiles(self: &Rc<Self>) {
         let current = self.keyboard_node.get();
         if matches!(