[dartdoc] Generics don't resolve in the analyzer.

[kallentu]

As seen in the comment here flutter/flutter#146652 (comment).
The analyzer doesn't seem to create the proper references any type in square brackets with generics, like [List<int>].

Dartdoc's comment reference resolution currently does have this feature and we would want to make sure this is supported before moving over to @docImports, since that will use the analyzer's resolution of comment references.

cc. @srawlins @goderbauer

[srawlins]

I dunno about "bug"; it was never designed to parse comment references with angle brackets. I think the language spec used to even specify that references were one identifier in [] or two identifiers separated by .. But it's no longer in the spec, so we added support for three identifiers.

I'd love to support type-argument-y things like [Map<String, List<int>>] and [void Function<T, S extends Future<T>>(S a)] and [(int record, {String type})].

See #47444 for other possible expansions (this is one of them).