Implement pure version of PaneGrid widget

native/src/widget/pane_grid/draggable.rs

@@ -0,0 +1,12 @@
+use crate::{Layout, Point};
+
+/// A pane that can be dragged.
+pub trait Draggable {
+    /// Returns whether the [`Draggable`] with the given [`Layout`] can be picked
+    /// at the provided cursor position.
+    fn can_be_dragged_at(
+        &self,
+        layout: Layout<'_>,
+        cursor_position: Point,
+    ) -> bool;
+}