glsl: Replace constant-index vector array accesses with swizzles

glsl: Replace constant-index vector array accesses with swizzles

Search and replace:

    ][0] -> ].x
    ][1] -> ].y
    ][2] -> ].z
    ][3] -> ].w

Fixes piglit tests inverse-mat[234].{vert,frag}.  These tests call the
inverse function with constant parameters and expect proper constant
folding to happen.  My suspicion is that this patch papers over some bug
in constant propagation involving array accesses.

Either way, all of these accesses eventually get lowered to swizzles.
This cuts out the middle man (saving a trivial amount of CPU).

NOTE: This is a candidate for the 9.1 branch.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Paul Berry <stereotype441@gmail.com>