`public_member_api_docs` ignores constructors in abstract interface classes

[Pante]

Describe the issue public_member_api_docs does not flag constructors in abstract interface classes that are undocumented.

To Reproduce

abstract interface class Foo {
  factory Foo.a() = Bar;
  
  factory Foo.b() => Bar();

  Foo();
}

class Bar extends Foo {}

Expected behavior The constructors should be flagged as undocumented, similar to how they are flagged in abstract & interface classes.