r300: fix variables detection for paired ALU and TEX instructions in different branches

r300: fix variables detection for paired ALU and TEX instructions in different branches

TEX instrutions can't write xyz and w to separate registers so we
need to create variables from them first, otherwise we can create
two variables from ALU writing the same register xyz and w in other
branch (this usually works when TEX is not present as the xyz and
w can read/write from different registers).

This fixes regalloc because the variables are later used as a
graph nodes.

The variable order should not matter but it slightly does (leading
to approx 0.3% shader-db temps increase as compared to previous
state), so just sort the variables list afterwards to be as close
to the previous behavior as possible and prevent the regression.

CC: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6936
Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Reviewed-by: Filip Gawin <filip@gawin.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17987>