Added PmfToQuantizedCdf op to contrib/coder in TensorFlow.

Added PmfToQuantizedCdf op to contrib/coder in TensorFlow.

The added op transforms probability mass functions (PMF) to quantized
cumulative distribution function (CDF), which can be used by range coder ops in
contrib/coder.

The op takes greedy approach to ensure that the post-quantization probability
masses do not sum over the maximum quantized value. The op does not make any
adjustment when the post-quantization probability masses already sum less than
the maximum value.

PiperOrigin-RevId: 192827779