nir: Switch to using 1-bit Booleans for almost everything

nir: Switch to using 1-bit Booleans for almost everything

This is a squash of a few distinct changes:

    glsl,spirv: Generate 1-bit Booleans

    Revert "Use 32-bit opcodes in the NIR producers and optimizations"

    Revert "nir/builder: Generate 32-bit bool opcodes transparently"

    nir/builder: Generate 1-bit Booleans in nir_build_imm_bool

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Tested-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>