Reworked Scrollable to account for lack of widget order guarantees.

Fixed thumb "snapping" bug on scrollable when cursor is out of bounds.

core/src/point.rs

@@ -75,3 +75,11 @@ impl std::ops::Sub<Point> for Point {
         Vector::new(self.x - point.x, self.y - point.y)
     }
 }
+
+impl std::ops::Add<Point> for Point {
+    type Output = Point;
+
+    fn add(self, point: Point) -> Point {
+        Point::new(self.x + point.x, self.y + point.y)
+    }
+}

core/src/rectangle.rs

@@ -111,6 +111,12 @@ impl Rectangle<f32> {
     }
 }
 
+impl std::cmp::PartialOrd for Rectangle<f32> {
+    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
+        (self.width * self.height).partial_cmp(&(other.width * other.height))
+    }
+}
+
 impl std::ops::Mul<f32> for Rectangle<f32> {
     type Output = Self;