Some backends may wish to reserve early uniforms for internal system values, and
use the remaining space for preamble storage. In this case, it's convenient to
teach nir_opt_preamble about a reserved offset. It's logical to treat the output
*size instead of an in/out variable that nir_opt_preamble adds to. This requires
a slight change to the consumers to zero the input.
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Acked-by-(with-sparkles): Asahi Lina <lina@asahilina.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20562>