48: Exposing `set_viewport_rect()` on `RenderPass`. r=kvark a=seivan Noticed that while viewport work with floats, scissors only work with unsigned integers. Not sure if relevant but [`width & height`](https://www.khronos.org/registry/OpenGL-Refpages/es2.0/xhtml/glViewport.xml) might not be able to be negative. Co-authored-by: Seivan Heidari <seivan.heidari@icloud.com>