Add `int64` axis support for `tf.cumsum` and `tf.cumprod` (#13791)

* Add `int64` axis support for `tf.cumsum` and `tf.cumprod`

This fix adds `int64` axis support for `tf.cumsum` and `tf.cumprod`.
Though `int64` is the registered data type for `axis` (`Tidx`), no
kernel is available.

The issue could be described as:
```
>>> import tensorflow as tf
>>> v = tf.cumsum([1, 2, 3], tf.constant(0, tf.int64))
>>> tf.Session().run(v)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 889, in run
    run_metadata_ptr)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 1120, in _run
    feed_dict_tensor, options, run_metadata)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 1317, in _do_run
    options, run_metadata)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/client/session.py", line 1336, in _do_call
    raise type(e)(node_def, op, message)
tensorflow.python.framework.errors_impl.InvalidArgumentError: No OpKernel was registered to support Op 'Cumsum' with these attrs.  Registered devices: [CPU], Registered kernels:
  device='CPU'; T in [DT_COMPLEX128]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_COMPLEX64]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_DOUBLE]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_FLOAT]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_HALF]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT8]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_UINT8]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT16]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_UINT16]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT32]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT64]; Tidx in [DT_INT32]

	 [[Node: Cumsum = Cumsum[T=DT_INT32, Tidx=DT_INT64, exclusive=false, reverse=false](Cumsum/x, Const)]]

Caused by op u'Cumsum', defined at:
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/ops/math_ops.py", line 2246, in cumsum
    x, axis, exclusive=exclusive, reverse=reverse, name=name)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/ops/gen_math_ops.py", line 1370, in cumsum
    name=name)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/op_def_library.py", line 787, in _apply_op_helper
    op_def=op_def)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/ops.py", line 2966, in create_op
    op_def=op_def)
  File "/usr/local/lib/python2.7/dist-packages/tensorflow/python/framework/ops.py", line 1473, in __init__
    self._traceback = self._graph._extract_stack()  # pylint: disable=protected-access

InvalidArgumentError (see above for traceback): No OpKernel was registered to support Op 'Cumsum' with these attrs.  Registered devices: [CPU], Registered kernels:
  device='CPU'; T in [DT_COMPLEX128]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_COMPLEX64]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_DOUBLE]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_FLOAT]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_HALF]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT8]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_UINT8]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT16]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_UINT16]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT32]; Tidx in [DT_INT32]
  device='CPU'; T in [DT_INT64]; Tidx in [DT_INT32]

	 [[Node: Cumsum = Cumsum[T=DT_INT32, Tidx=DT_INT64, exclusive=false, reverse=false](Cumsum/x, Const)]]

>>>
```

This fix adds the missing kernel.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add test cases for `int64` axis support of `tf.cumsum` and `tf.cumprod`

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Reformat scan_ops.cc with `clang-format -i`

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>