ac/nir: Implement NGG deferred attribute culling in NIR.

ac/nir: Implement NGG deferred attribute culling in NIR.

Culling is traditionally done by the rasterizer, but that
can be a bottleneck when an app creates a large number
of primitives. Eg. a lot of tiny triangles reduce the
rasterziation efficiency.

NGG makes it possible for the shader to check primitives
and delete those that it can prove are not needed.

After this is done, we have to repack the surviving invocations
so they remain compact. This also saves bandwidth, because
some memory loads are only executed by those vertices that
survived the culling.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10525>