message: Implement `Widget::overlay` for `Row`
diff: use std::hash::Hash;
  use crate::{
  - layout, Align, Clipboard, Element, Event, Hasher, Layout, Length, Point,
  - Widget,
  + layout, Align, Clipboard, Element, Event, Hasher, Layout, Length, Overlay,
  + Point, Widget,
  };
  use std::u32;
  @@ -206,6 +206,17 @@ where
  child.widget.hash_layout(state);
  }
  }
  +
  + fn overlay(
  + &mut self,
  + layout: Layout<'_>,
  + ) -> Option<Overlay<'a, Message, Renderer>> {
  + self.children
  + .iter_mut()
  + .zip(layout.children())
  + .filter_map(|(child, layout)| child.widget.overlay(layout))
  + .next()
  + }
  }
  /// The renderer of a [`Row`].
  