Make Overlay aware of viewport

... and unify `Image::float` and `Image::translate`

widget/src/button.rs

@@ -432,12 +432,14 @@ where
         tree: &'b mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
+        viewport: &Rectangle,
         translation: Vector,
     ) -> Option<overlay::Element<'b, Message, Theme, Renderer>> {
         self.content.as_widget_mut().overlay(
             &mut tree.children[0],
             layout.children().next().unwrap(),
             renderer,
+            viewport,
             translation,
         )
     }