nir: Allow nir_opt_algebraic to see booleanness through &&, ||, ^, !.

nir: Allow nir_opt_algebraic to see booleanness through &&, ||, ^, !.

We have some useful optimizations to drop things like 'ine a, 0' on a
boolean argument, but if 'a' came from logical operations on bools, it
couldn't tell.  These kinds of constructs appear as a result of TGSI->NIR
quite frequently (at least with if flattening), so being a little more
aggressive in detecting booleans can pay off.

v2: Add ixor as a booleanness-preserving op (Suggestion by Connor).

vc4 results:
total instructions in shared programs: 40207 -> 39881 (-0.81%)
instructions in affected programs:     6677 -> 6351 (-4.88%)

Reviewed-by: Matt Turner <mattst88@gmail.com> (v1)
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>