Add fixed-point thresholding support

[SpiritSeeker]

Add fixed-point datatype support for thresholding layers.

• extend RoundAndClipThresholds transform to operate with fixed-point inputs. The thresholds are rounded to have the same number of fractional bits as the input.
• restrict RTL implementation to run only when both fixed-point inputs and thresholds have same number of fractional bits, i.e., it is equivalent to comparing their integer representations.