new lookup system seems to miss reexports/canonicalization of function typedefs

[jcollins-g]

This results in some ambiguity as in this case for flutter:

  warning: reference lookup resolution differs between lookup implementations:  [WidgetBuilder] => new: element: [framework.WidgetBuilder] warn: true old: element: [widgets.WidgetBuilder] warn: true
    from cupertino.CupertinoApp.routes: (file:///Users/jcollins/dart/flutter/packages/flutter/lib/src/cupertino/app.dart:249:37)
    from documentation for symbol cupertino.CupertinoApp.routes: (file:///Users/jcollins/dart/flutter/packages/flutter/lib/src/cupertino/app.dart:249:37)

This can be worked around by specifying the correct library, but is not ideal.

[srawlins]

This may have been the case of #3070