`Go to imports` doesn't work on annotations constructors

[FMorschel]

Repro:

import 'package:meta/meta.dart';

@Immutable()
class C {}

If it is prefixed, it works fine. This is probably a missed case.

[FMorschel]

Here is the CL for this https://dart-review.googlesource.com/c/sdk/+/468900