Add a _typeshed.pyi file and a PathLike alias (#4161)

stdlib/2and3/_typeshed/__init__.pyi

@@ -0,0 +1,28 @@
+# Utility types for typeshed
+
+# This module contains various common types to be used by typeshed. The
+# module and its types do not exist at runtime. You can use this module
+# outside of typeshed, but no API stability guarantees are made. To use
+# it in implementation (.py) files, the following construct must be used:
+#
+#     from typing import TYPE_CHECKING
+#     if TYPE_CHECKING:
+#         from _typeshed import ...
+#
+# If on Python versions < 3.10 and "from __future__ import annotations"
+# is not used, types from this module must be quoted.
+
+import sys
+from typing import Text, Union
+
+# StrPath and AnyPath can be used in places where a
+# path can be used instead of a string, starting with Python 3.6.
+if sys.version_info >= (3, 6):
+    from os import PathLike
+    StrPath = Union[str, PathLike[str]]
+    BytesPath = Union[bytes, PathLike[bytes]]
+    AnyPath = Union[str, bytes, PathLike[str], PathLike[bytes]]
+else:
+    StrPath = Text
+    BytesPath = bytes
+    AnyPath = Union[Text, bytes]