nir: Keep the range analysis HT around intra-pass until we make a change.

nir: Keep the range analysis HT around intra-pass until we make a change.

This lets us memoize range analysis work across instructions.  Reduces
runtime of shader-db on Intel by -30.0288% +/- 2.1693% (n=3).

Fixes: 405de7ccb6cb ("nir/range-analysis: Rudimentary value range analysis pass")
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>