nir/builder: Emit x != 0 for nir_i2b

nir/builder: Emit x != 0 for nir_i2b

There are a lot of optimizations in opt_algebraic that match ('ine', a,
0), but there are almost none that match i2b.  Instead of adding a huge
pile of additional patterns (including variation that include both ine
and i2b), just emit a != 0 instead of i2b(a).

I think that the changes to the unit tests weaken them slightly, but
perhaps that's okay?

No shader-db changes on any Intel platform.  The GLSL paths use other
means to generate i2b operations, but the SPIR-V paths use nir_i2b.
Presumably since 4676b3d3dd9 (nir: Use nir_test_mask instead of
i2b(iand)), no fossil-db changes either.

v2: Use nir_ine_imm.  Suggested by Jesse.

Acked-by: Jesse Natalie <jenatali@microsoft.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15121>