nir: Add a small pass to rematerialize derefs per-block

This pass re-materializes deref instructions on a per-block basis to
ensure that every use of a deref occurs in the same block as the
instruction which uses it.

Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Cc: "18.2" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 7d1d1208)
[Juan A. Suarez: resolve trivial conflicts]
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>

Conflicts:
	src/compiler/nir/nir_deref.c

Squashed with:

nir: add initializer data to fix MSVC compile error

CC: Jason Ekstrand <jason@jlekstrand.net>
Fixes: 82799a5d1b8 ("nir: Add a small pass to rematerialize derefs
per-block")
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>

(cherry picked from commit 0c82e360)