Documentation for functions in `enum`s are linked but not generated

[mkorbel1]

If you define an enum with a function in it, then the documentation page for that enum will have a link to a documentation page about that function (and even the doc comment for the function), however the page for the function will be missing.

In addition, since the target of the link is missing, --validate-links will trigger a warning. This was annoying to debug because of #3331. I had to run this repo in debug mode and add print statements to figure out what was missing since I didn't know what the warning was.

To reproduce, create an enum with a static function in it, for example:

enum MyEnum {
  a,
  b,
  c;

  /// Says hello!
  static void myFunction() {
    print("hello");
  }
}

The generated documentation will include MyEnum and a link to myFunction, as expected, however the link (circled) will be dead because the doc page for myFunction is not generated.

[srawlins]

Sorry for the extreme delay (dartdoc has fallen through the gaps in our triage process). I think there is a sizeable blind spot here with enhanced enums. I noticed that dartdoc's Enum doesn't inherit from Class, but it really probably should.