Deprecate dict usage of SelectableGroups.

Author: jaraco

importlib_metadata/__init__.py

@@ -252,7 +252,7 @@ def values(self):
         return super().values()
 
 
-class SelectableGroups(dict):
+class SelectableGroups(Deprecated, dict):
     """
     A backward- and forward-compatible result from
     entry_points that fully implements the dict interface.
@@ -270,7 +270,8 @@ def _all(self):
         """
         Reconstruct a list of all entrypoints from the groups.
         """
-        return EntryPoints(itertools.chain.from_iterable(self.values()))
+        groups = super(Deprecated, self).values()
+        return EntryPoints(itertools.chain.from_iterable(groups))
 
     @property
     def groups(self):