st/nine: Prepare constant compaction in nine_shader

st/nine: Prepare constant compaction in nine_shader

When indirect addressing is not used, we know exactly
which constants are accessed, and thus can
have them located in consecutive slots.
We thus parse again the shader with a slot map
for compaction.

The path contains the work inside nine_shader.c for this
path, but it needs some other commits to work, and thus
is not enabled yet by this commit.

Signed-off-by: Axel Davy <davyaxel0@gmail.com>