Allow Gradient in Rectangle border and ShapePath stroke

As far as I can tell, there's no way to draw a Rectangle border or a ShapePath stroke with a gradient.

But the code obviously exists somewhere (QPainter and Canvas can do it), so it doesn't seem to make any sense.

Maybe there's some internal reason that drawing a gradient border is less efficient. But that doesn't change the fact that I need a rectangle to have a gradient border, so I'm just forced to do it extremely inefficiently (Canvas) or get someone to make a custom C++ item to do it. Both of those options are much worse than Qt just doing it automatically, possibly with a note in the docs that it's a little bit slower than a solid colored stroke.