[*.py] Rename "Arguments:" to "Args:"

[SamuelMarks]

EDIT: I understand your format is some custom one, not the Google one. So not sure, maybe this should be closed, or maybe everything should be conformed to Args?

I've written custom parsers and emitters for everything from docstrings to classes and functions. However, I recently came across an issue with the TensorFlow codebase: inconsistent use of Args: and Arguments: in its docstrings. It is easy enough to extend my parsers to support both variants, however it looks like Arguments: is wrong anyway, as per:

• https://google.github.io/styleguide/pyguide.html#doc-function-args @ ddccc0f

• https://chromium.googlesource.com/chromiumos/docs/+/master/styleguide/python.md#describing-arguments-in-docstrings @ 9fc0fc0

• https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html @ c0ae8e3

Therefore, only Args: is valid. This PR replaces them throughout the codebase.

PS: For related PRs, see tensorflow/tensorflow/pull/45420