draw: use stdint.h types

draw: use stdint.h types

Here, we want explicitly sized types, not just types that happen to be
of the right size.

Reviewed-by: Eric Engestrom <eric@igalia.com>
Reviewed-by: Yonggang Luo <luoyonggang@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23833>