Unable to link to top-level property from doc comments

[sethladd]

Notice how NAME_SINGLEUNDERSCORE is not linked.

Bug is here:

  Library refLibrary;
  var e = refElement is ClassMemberElement ||
          refElement is PropertyAccessorElement
      ? refElement.enclosingElement
      : refElement;

  // If e is a ParameterElement, it's
  // never going to be in a library. So refLibrary is going to be null.
  refLibrary = element.package.libraries.firstWhere(
      (lib) => lib.hasInNamespace(e), orElse: () => null);

In the case of a top-level property accessor, we shouldn't be getting its enclosingElement... that will never be in the namespace of a library.

[sethladd]

OK, managed to fix this one. Not fun. :( CommentRefs from the analyzer can return a PropertyAccessorElement for a top-level const, so we need to pop out the top-level const so the rest of the machinery works.

But, on the plus side, managed to delete some duplicate code.