Make alignment a widget property

src/widget/position/pad.rs

@@ -8,7 +8,7 @@ pub struct Pad {
 impl Widget for Pad {
     fn draw(&mut self, painter: &mut Painter) -> Size {
         let inner = painter
-            .widget_within(&self.inner, self.padding.region())
+            .widget_aligned(&self.inner, self.padding.region(), RegionAlign::NEAR)
             .size();
         Size {
             x: Len {