Buildable types don't get setters accepting Builders when Builder is package private

[aabdagic]

When not part of the same package, that's necessary to avoid compile time errors, but here they are part of the same package. Note that I tested this on a composed @FreeBuilder type, not on other buildable types.

For example, this won't work because setNested2 doesn't have a overload that accepts a Nested2.Builder.

public class Foo {

  void test() {
    new Nested1.Builder().setNested2(new Nested2.Builder());
  }

  @FreeBuilder
  abstract static class Nested1 {
    abstract Nested2 getNested2();
    static class Builder extends Foo_Nested1_Builder {}
  }

  @FreeBuilder
  abstract static class Nested2 {
    static class Builder extends Foo_Nested2_Builder {}
  }
}

But if make Nested2.Builder public, even without making Nested2 public, i.e.

  @FreeBuilder
  abstract static class Nested2 {
    public static class Builder extends Foo_Nested2_Builder {}
  }

the setter is generated.