CEPL image format completeness (sampler checks)

[cbaggers]

Assert the following in the sampler:

Image format completeness

The internal format a texture uses can also affect its completeness, depending on its sampling parameters.

Integer color formats and stencil index formats (whether GL_STENCIL_INDEX directly or via Stencil Texturing) do not support linear filtering. As such, the GL_TEXTURE_MAG_FILTER sampling parameter must be GL_NEAREST, and GL_TEXTURE_MIN_FILTER must be either GL_NEAREST or GL_NEAREST_MIPMAP_NEAREST.

https://www.khronos.org/opengl/wiki/Texture#Image_format_completeness