fix PathDistribution._normalized_name implementation

- apply PEP 503 normalization to the extracted names
  (e.g.: `zope..inter_face-4.2.dist-info` must yield
   the name `zope_inter_face`)

`entry_points(…)` can yield the entry-points
of a shadowed distribution. For example: with a version of `mypkg`
in the system' site-packages directory when working from another
development checkout of the same package (with a `mypkg.egg-info`
directory mishandled by the first bug).

Author: benoit-pierre

importlib_metadata/__init__.py

@@ -956,7 +956,10 @@ def _normalized_name(self):
         normalized name from the file system path.
         """
         stem = os.path.basename(str(self._path))
-        return self._name_from_stem(stem) or super()._normalized_name
+        return (
+            pass_none(Prepared.normalize)(self._name_from_stem(stem))
+            or super()._normalized_name
+        )
 
     @staticmethod
     def _name_from_stem(stem):