Support navigation from unnamed constructor (`.new`)

[parlough]

Is your feature request related to a problem? Please describe.

When on an unnamed constructor reference (such as new in Test.new below), "Go to declaration" results in "Cannot find declaration to go to". It does however work for named constructors.

class Test {
  Test();
}

void main() {
  print(Test.new);
  //          ^ Navigate from here
}

Describe the solution you'd like.

I'd expect this to navigate to the Test() constructor if present. If not present, I'd expect it to the navigate me to the class declaration/name. Thanks!

Additional context:

Navigating from the unnamed constructor does work in LSP-based editors.