This op determines the maximum scale_factor that would map the initial
[input_min, input_max] range to a range that lies within the representable
quantized range.

It determines the scale from one of input_min and input_max, then updates the
other one to maximize the representable range.

e.g.

*   if the output is signed, num_bits = 8, [input_min, input_max] = [-10.0,

        `tf.GradientTape` inside a `tf.function`.
    *   Changed the default step size in `gradient_checker_v2.compute_gradients`
        to be exactly representable as a binary floating point numbers. This
        avoids poluting gradient approximations needlessly, which is some cases
        leads to false negatives in op gradient tests.