nir/print: Improve output of NIR_DEBUG=print_consts and make it default

The general plan here is:

• Make nir_gather_ssa_types() just ignore non-SSA values.
• Change inline print to include only one terse representation, use the pass above to help decision.
• Flip the default.

More details on the respective commit messages.

UPDATE: In addition to that, there's patches to pull out some logic from gather_ssa_types ("what's the type of this intrinsic source") and use that in nir_print too. See comments below (or the commit message) about breaking a tie.

---

Before and after comparisons from the second commit:

For illustration, here's some instructions from crucible test func.shader.averageRounded.uint64_t with NIR_DEBUG=print_consts:

BEFORE:

vec1 32 con ssa_23 = load_const (0xfffffffc = -nan)
vec1 32 div ssa_24 = iand ssa_13, ssa_23 /*(0xfffffffc = -nan)*/
vec1 32 con ssa_25 = load_const (0x00000024 = 0.000000)
vec1 32 con ssa_26 = intrinsic load_ubo (ssa_1 /*(0x00000002 = 0.000000)*/, ssa_25 /*(0x00000024 = 0.000000)*/) (access=0, align_mul=1073741824, align_offset=36, range_base=0, range=-1)
vec1 32 con ssa_27 = load_const (0x00000008 = 0.000000)
vec1 32 con ssa_28 = load_const (0x00000007 = 0.000000)
vec1 32 con ssa_29 = iand ssa_4.y, ssa_1 /*(0x00000002 = 0.000000)*/
vec1 32 con ssa_30 = ishl ssa_29, ssa_28 /*(0x00000007 = 0.000000)*/
vec1 32 con ssa_31 = load_const (0x7b000808 = 664776890994587263929995856502063104.000000)
vec1 32 con ssa_32 = ior ssa_31 /*(0x7b000808 = 664776890994587263929995856502063104.000000)*/, ssa_30

AFTER:

vec1 32 con ssa_23 = load_const (0xfffffffc = -nan)
vec1 32 div ssa_24 = iand ssa_13, ssa_23 (0xfffffffc)
vec1 32 con ssa_25 = load_const (0x00000024 = 0.000000)
vec1 32 con ssa_26 = intrinsic load_ubo (ssa_1 (0x2), ssa_25 (0x24)) (access=0, align_mul=1073741824, align_offset=36, range_base=0, range=-1)
vec1 32 con ssa_27 = load_const (0x00000008 = 0.000000)
vec1 32 con ssa_28 = load_const (0x00000007 = 0.000000)
vec1 32 con ssa_29 = iand ssa_4.y, ssa_1 (0x2)
vec1 32 con ssa_30 = ishl ssa_29, ssa_28 (0x7)
vec1 32 con ssa_31 = load_const (0x7b000808 = 664776890994587263929995856502063104.000000)
vec1 32 con ssa_32 = ior ssa_31 (0x7b000808), ssa_30

and some instructions from crucible test func.gs.basic with NIR_DEBUG=print_consts, now showing float representation being selected:

BEFORE:

vec4 32 ssa_10 = load_const (0x3e4ccccd, 0x3e4ccccd, 0x00000000, 0x00000000) = (0.200000, 0.200000, 0.000000, 0.000000)
vec4 32 ssa_9 = intrinsic load_deref (ssa_42) (access=0)
vec4 32 ssa_11 = fadd ssa_9, ssa_10 /*(0x3e4ccccd, 0x3e4ccccd, 0x00000000, 0x00000000) = (0.200000, 0.200000, 0.000000, 0.000000)*/

AFTER:

vec4 32 ssa_10 = load_const (0x3e4ccccd, 0x3e4ccccd, 0x00000000, 0x00000000) = (0.200000, 0.200000, 0.000000, 0.000000)
vec4 32 ssa_9 = intrinsic load_deref (ssa_42) (access=0)
vec4 32 ssa_11 = fadd ssa_9, ssa_10 (0.200000, 0.200000, 0.000000, 0.000000)