Add a new pass in eevee

this pass will render a number of spheres

• uses DRW_viewport_matrix_override_set to set the camera to a default location
• uses a copy of the DefaultLitPass to render the 2 spheres + color palette
• uses backculling so no depth check is needed.
• render it during fx (or after)
• use GPU_framebuffer_viewport_set to render the spheres in the corner
• before rendering set num_lights to 0 so no shadows and lights are calculated during this call.

TODO:

• when pressing N and transparency is turned on, the lookdev balls should slide with the sidebar
• rendering the background should be an option
• option to disable the lights completely
• default diffuse ball should be less shiny