glsl_to_tgsi: separate immediates from array constants during IR translation

glsl_to_tgsi: separate immediates from array constants during IR translation

Before, if any uniform or constant array was accessed with indirect
addressing, st_translate_program() would emit uniform constants in the place
of immediates.  This behavior was unavoidable with ir_to_mesa/mesa_to_tgsi, but
glsl_to_tgsi can work around it since the GLSL IR backend and the TGSI
emission are both inside the state tracker.