UPx shape drawing is incompatible with scrolled clipping

[ecton]

While working on refactoring the Scroll widget to use UPx for some of its values before exposing them on the public API, I realized that the calculation in Graphics::draw_shape converting a negative translation into UPx will be a lossy conversion that will cause the shape to render at 0,0 rather than offset correctly.

This is not a Kludgine problem as Kludgine requires clip rects to be UPx, and the invention of negative space is done in Cushy.