Avoid illegal copies. This intercepts the last step of a copy to avoid
generating validation errors or corrupting the driver on some instances.
We can create views and emit copies accordingly in future commits and
remove this last-step validation.
Add a flat table to test if it's legal to create a texture view between
two formats or copy betweem them.
This table is based on ARB_copy_image and ARB_texture_view. Copies are
more permissive than views.