arb_gpu_shader5: Add some initial tests for d/u sampler array indexing

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
arb_gpu_shader5: Add more tests for sampler array indexing

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
arb_gs5: add nonconst sampler access tests

These test some of the annoying cases of fermi/kepler instruction
encodings.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>