[*.py] Rename "Arguments:" to "Args:" (#49736)

Summary:
I've written custom parsers and emitters for everything from docstrings to classes and functions. However, I recently came across an issue when I was parsing/generating from the TensorFlow codebase: inconsistent use of `Args:` and `Arguments:` in its docstrings.

```sh
(pytorch#c348fae)$ for name in 'Args:' 'Arguments:'; do
    printf '%-10s %04d\n' "$name" "$(rg -IFtpy --count-matches "$name" | paste -s -d+ -- | bc)"; done
Args:      1095
Arguments: 0336
```

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://github.com/google/styleguide/blob/ddccc0f/pyguide.md)

  - https://chromium.googlesource.com/chromiumos/docs/+/master/styleguide/python.md#describing-arguments-in-docstrings @ [`9fc0fc0`](https://chromium.googlesource.com/chromiumos/docs/+/9fc0fc0/styleguide/python.md)

  - https://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html @ [`c0ae8e3`](https://github.com/sphinx-contrib/napoleon/blob/c0ae8e3/docs/source/example_google.rst)

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

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

PPS: The trackbacks automatically appearing below are sending the same changes to other repositories in the [PyTorch](https://github.com/pytorch) organisation.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/49736

Reviewed By: albanD

Differential Revision: D25710534

Pulled By: soumith

fbshipit-source-id: 61e8ff01abb433e9f78185c2d1d0cbd7c22c1619

torch/_lobpcg.py

@@ -76,7 +76,7 @@ def _polynomial_value(poly, x, zero_power, transition):
     """
     A generic method for computing poly(x) using the Horner's rule.
 
-    Arguments:
+    Args:
       poly (Tensor): the (possibly batched) 1D Tensor representing
                      polynomial coefficients such that
                      poly[..., i] = (a_{i_0}, ..., a{i_n} (==1)), and
@@ -384,7 +384,7 @@ def lobpcg(A: Tensor,
       we do the following symmetrization map: `A -> (A + A.t()) / 2`.
       The map is performed only when the `A` requires gradients.
 
-    Arguments:
+    Args:
 
       A (Tensor): the input tensor of size :math:`(*, m, m)`
 
@@ -925,7 +925,7 @@ class LOBPCG(object):
           matrix product `D M` with element-wise product `M *
           d`. Also, creating the diagonal matrix `D` is avoided.
 
-        Arguments:
+        Args:
         S (Tensor): the matrix basis for the search subspace, size is
                     :math:`(m, n)`.
 
@@ -957,7 +957,7 @@ class LOBPCG(object):
                   modification of the corresponding algorithm
                   introduced in [StathopolousWu2002].
 
-        Arguments:
+        Args:
 
           U (Tensor) : initial approximation, size is (m, n)
           drop (bool) : when True, drop columns that
@@ -1023,7 +1023,7 @@ class LOBPCG(object):
         .. note:: If all U columns are B-collinear to V then the
                   returned tensor U will be empty.
 
-        Arguments:
+        Args:
 
           U (Tensor) : initial approximation, size is (m, n)
           V (Tensor) : B-orthogonal external basis, size is (m, k)