nir: Add a printf lowering pass (v5)

nir: Add a printf lowering pass (v5)

This pass creates a SSBO var for the printf buffer. It does an atomic increment
at the beginning of the buffer to determine where to write, then dumps
the args after that.

v2: [airlied]
Enhanced to use an index into a set of format info that is passed
back to the caller. The format info contains the number of args,
argument sizes and the format string.

v3: move format string lowering to vtn

v4: Jason reworked it.

v5: assume buffer has initial offset prebaked in and work from there.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8254>