super param support for library_private_types_in_public_api

[pq]

See: #3131

/cc @bwilkerson

[coveralls]

Coverage decreased (-0.003%) to 94.234% when pulling fc0502b on library_private_types_in_public_api_super_params into f4d926d on master.

[bwilkerson]

What about the following case:

class _O extends Object {}
class _A {
  _A(_O o);
}
class B extends _A {
  B(super.o); // lint?
}

My expectation is that this would also be flagged, even though the type of the parameter is implicit rather than explicit, but I don't think the code as written will catch it.