clip: add Path method to Rect

Useful when drawing non-rounded rectangles with Stroke.
Also, this makes it consistent with RRect and Circle which
also have a Path method.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

op/clip/shapes.go

@@ -18,10 +18,7 @@ type Rect image.Rectangle
 func (r Rect) Op() Op {
 	return Op{
 		outline: true,
-		path: PathSpec{
-			shape:  ops.Rect,
-			bounds: image.Rectangle(r),
-		},
+		path:    r.Path(),
 	}
 }
 
@@ -30,6 +27,14 @@ func (r Rect) Push(ops *op.Ops) Stack {
 	return r.Op().Push(ops)
 }
 
+// Path returns the PathSpec for the rectangle.
+func (r Rect) Path() PathSpec {
+	return PathSpec{
+		shape:  ops.Rect,
+		bounds: image.Rectangle(r),
+	}
+}
+
 // UniformRRect returns an RRect with all corner radii set to the
 // provided radius.
 func UniformRRect(rect f32.Rectangle, radius float32) RRect {