Add more complete type hints for pkg_resources. (#2433)

The current file only covers pkg_resources/__init__.py.
pkg_resources/py31compat.pyi is used by setuptools, for example.

third_party/3/pkg_resources/py31compat.pyi

@@ -0,0 +1,14 @@
+from typing import Text
+import os
+import sys
+
+needs_makedirs: bool
+
+def _makedirs_31(path: Text, exist_ok: bool = ...) -> None: ...
+
+# _makedirs_31 has special behavior to handle an edge case that was removed in
+# 3.4.1. No one should be using 3.4 instead of 3.4.1, so this should be fine.
+if sys.version_info >= (3,):
+    makedirs = os.makedirs
+else:
+    makedirs = _makedirs_31