Sync docstring of preprocess_input with _preprocess_numpy_input and _preprocess_symbolic_input in imagenet_utils.py (#10006)

* fix cntk static learning phase issue; add a test

* fix code style;add more comments

* add boolean support

* fix code style issue

* Allow shift_range to be 1-D array-like or int

* Add docstrings

* Fix conflict resolution merge minor disaster

* remove stray line from merge

* Remove extra "tabs"

* Added an error message for undefined shape on NASNet.

* Forgot that the message should be present only when loading imagenet weights.

* Changed the message.

* Add support fot `constants` in Bidirectional wrapper

* Add more tests for Bidirectional wrapper

* Fix `compute_mask` for Birectional with return_state=True

Fix `compute_mask` to properly support `return_state` introduced in Birectional with #8977

* Add test for Bidirectional with unknown timestamps

* Skip test for CNTK for unknown timestamps with Bidirectional

* avoid override the input constant when need broadcast sequential axis on rnn's constant

* Move _standardize_args to recurrent, remove duplication

* Fix  for Birectional when multiple masks are passed

* Added notes to manually install h5py if needed

* Added FAQ entry on h5py

* deleted redundant remark about h5py

* updated FAQ to reflect dependency change

* fixed comment format to pass failing test

* removed new trailing whitespaces

* improved docstring format

* reverted callbacks.py

* fixed links in model.py

* updated faq.py

* link pointing to FAQ

Signed-off-by: NCUI Wei <ghostplant@qq.com>

The way the documentation is parsed for the Keras website made some lines of the documentation beginning with "Default:" look funny. Also changed the documentation of return value to be clear that it always returns a batch of images.

* REL: bump to `pydot >= 1.2.4` in `extras_require`

* MAI: import pydot (as required in `extras_require`)

* MAI: refine error messages for `pydot` and GraphViz

distinguish between absence of `pydot` and failure to find
the executables of GraphViz in the $PATH.

* DEV: ignore `.pytest_cache`

* Removed generate dropout ones from recurrent.

* Fixed index issue.

* Fixed the NASNet issue.

* Nasnet doesn't require flatten.

* Updated documentation accordingly.

Currently, `fit/evaluate_generator` don't support this case without this fix.
But framework-native data tensors are already supported by `_fit_loop` and `_test_loop`.
Signed-off-by: NCUI Wei <ghostplant@qq.com>

* Add kwarg and documentation for dilation_rate to SeparableConvs

* Fix pep8 complaint

I forgot to check the style before committing. Pep8 was complaining about a missing whitespace after comma, now it's fixed.

* Document that `"same"` is inconsistent across backends with `strides` != 1

* Use "[here](...)"

* Add documentation for 'subset' argument (flow and flow_from_directory) and for 'interpolation' argument (flow_from_directory)

* Fix style for 'flow' and 'flow_from_directory' ImageDataGenerator methods doc

* Add support for class methods documentation

* Documentation: remove the need of external CNN and JS files, using plain markdown

* Documentation: allow to decide which class method to document using a string or a fully qualified name

* Documentation: remove the need of a custom theme

Signed-off-by: NCUI Wei <ghostplant@qq.com>