gh-62534: Document that three-argument type() does not call __prepare__ (GH-154028)

gh-62534: Document that three-argument type() does not call __prepare__ (GH-154028)

The three-argument form of type() skips the metaclass __prepare__
method, which is called by the class statement machinery rather than
by the metaclass call itself. Say so in the type() entry and point to
types.new_class() for dynamic class creation with the appropriate
metaclass, as directed in the issue thread.