nir/range-analysis: Range tracking for fpow

nir/range-analysis: Range tracking for fpow

One shader from Metro Last Light and the rest from Rochard.  In the
Rochard cases, something like:

    min(1.0, max(pow(saturate(x), y), z))

was transformed to

    saturate(max(pow(saturate(x), y), z))

because the result of the pow must be >= 0.

The Metro Last Light case was similar.  An instance of

    min(pow(abs(x), y), 1.0)

became

    saturate(pow(abs(x), y))

v2: Fix some comments.  Suggested by Caio.

v3: Fix setting is_intgral when the exponent might be negative.  See
also Mesa MR !1778.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
All Intel platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 16280670 -> 16280659 (<.01%)
instructions in affected programs: 1130 -> 1119 (-0.97%)
helped: 11
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 0.72% max: 1.43% x̄: 1.03% x̃: 0.97%
95% mean confidence interval for instructions value: -1.00 -1.00
95% mean confidence interval for instructions %-change: -1.19% -0.86%
Instructions are helped.

total cycles in shared programs: 367168430 -> 367168270 (<.01%)
cycles in affected programs: 10281 -> 10121 (-1.56%)
helped: 10
HURT: 1
helped stats (abs) min: 16 max: 18 x̄: 17.00 x̃: 17
helped stats (rel) min: 1.31% max: 2.43% x̄: 1.79% x̃: 1.70%
HURT stats (abs)   min: 10 max: 10 x̄: 10.00 x̃: 10
HURT stats (rel)   min: 3.10% max: 3.10% x̄: 3.10% x̃: 3.10%
95% mean confidence interval for cycles value: -20.06 -9.04
95% mean confidence interval for cycles %-change: -2.36% -0.32%
Cycles are helped.