*   `pfor/vectorized_map`: Added support for vectorizing 56 more ops.
        Vectorizing `tf.cond` is also supported now.
    *   Set as much partial shape as we can infer statically within the gradient
        impl of the gather op.
    *   Gradient of `tf.while_loop` emits `StatelessWhile` op if `cond` and body
        functions are stateless. This allows multiple gradients while ops to run
        in parallel under distribution strategy.

of this function. Note, in some cases
`m` could be equal to `n`, but this need not be the case. Each
range specification entry can be one of the following:

- An ellipsis (...). Ellipses are used to imply zero or more
  dimensions of full-dimension selection and are produced using
  `ellipsis_mask`. For example, `foo[...]` is the identity slice.

- A new axis. This is used to insert a new shape=1 dimension and is