The `data_format` attr specifies the layout of the input and output tensors
with the following options:
  "NHWC": `[ batch, height, width, channels ]`
  "NCHW": `[ batch, channels, height, width ]`
  "NCHW_VECT_C":
      `qint8 [ batch, channels / 4, height, width, 4 ]`

It is useful to consider the operation as transforming a 6-D Tensor.
e.g. for data_format = NHWC,

    *   Allow sparse float splits to support multivalent feature columns.
    *   Add `quantile` to `tf.distributions.TransformedDistribution`.
    *   Add `NCHW_VECT_C` support for `tf.depth_to_space` on GPU.
    *   Add `NCHW_VECT_C` support for `tf.space_to_depth` on GPU.

## API Changes

*   Rename `SqueezeDims` attribute to `Axis` in C++ API for Squeeze op.