turnip: force sample interpolations for sample shading

Sample shading has similiar definitions in Vulkan and OpenGL, and they
both require unique associated data.  While the definition for Vulkan
might change, we should stick to the current definition until the change
takes place and until apps (i.e., ANGLE) are updated.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16700>
3 files changed