nir: propagate bitsize information in nir_search

nir: propagate bitsize information in nir_search

When we replace an expresion we have to compute bitsize information for the
replacement. We do this in two passes to validate that bitsize information
is consistent and correct: first we propagate bitsize from child nodes to
parent, then we do it the other way around, starting from the original's
instruction destination bitsize.

v2 (Iago):
- Always use nir_type_bool32 instead of nir_type_bool when generating
  algebraic optimizations. Before we used nir_type_bool32 with constants
  and nir_type_bool with variables.
- Fix bool comparisons in nir_search.c to account for bitsized types.

v3 (Sam):
- Unpack the double constant value as unsigned long long (8 bytes) in
nir_algrebraic.py.

v4 (Sam):
- Use helpers to get type size and base type from nir_alu_type.

Signed-off-by: Iago Toral Quiroga <itoral@igalia.com>
Signed-off-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>