add rolling window batch operation for tf.data.Dataset (#16123)

* ENH: add slide_dataset_op

* TST: add test case

* DOC: add docment

* CLN: implement sliding_window_batch

* CLN: hiddent SlideDataset

* CLN: remove Dataset.slide

* DOC: 2017 -> 2018

* CLN: use push_back

* DOC: drop the final smaller block

* CLN: rename slide_size -> window_size

* CLN: rename slide_step -> stride

* DOC: no default for stride at c++ side

* DOC: revise comments

* BLD: expose sliding_window_batch API

* CLN: code style

* DOC: revise documents

* CLN: move to IteratorContext

* TST: remove contrib.dataset_ops

* DOC: move desp to api def

* CLN: fix python 2 indent

* DOC: used by core.apply method