Fix #9648: autodoc: *args and **kwargs entries are duplicated

In basic usage of autodoc (docstring), `args` and `kwargs` arguments
are marked up without stars.  But numpydoc style recommends to mark
them up with stars.

This adds support for starred arguments in docstrings to
`autodoc_typehints` feature.

tests/roots/test-ext-napoleon/conf.py

@@ -0,0 +1,5 @@
+import os
+import sys
+
+sys.path.insert(0, os.path.abspath('.'))
+extensions = ['sphinx.ext.napoleon']

tests/roots/test-ext-napoleon/index.rst

@@ -0,0 +1,6 @@
+test-ext-napoleon
+=================
+
+.. toctree::
+
+   typehints

tests/roots/test-ext-napoleon/mypackage/typehints.py

@@ -0,0 +1,11 @@
+def hello(x: int, *args: int, **kwargs: int) -> None:
+    """
+    Parameters
+    ----------
+    x
+        X
+    *args
+        Additional arguments.
+    **kwargs
+        Extra arguments.
+    """

tests/roots/test-ext-napoleon/typehints.rst

@@ -0,0 +1,5 @@
+typehints
+=========
+
+.. automodule:: mypackage.typehints
+   :members: