Screen Position shares TextCoord coordinate space

ScreenPosition is not updating when the viewport is resized. As the viewport is made larger, screen position scales to match this larger area. As the viewport is made smaller, screen position continues to use the maximum size the viewport ever reached.

1. Open any project in the editor.
2. Create a material with the setup depicted in the screenshot attached to this bug.
3. Apply the material to an unbound post processing volume in the viewport.
4. Resize the viewport to be larger
5. Resize the viewport to be smaller.

Result:
Observe that the screen position does not resize with the viewport.