[analyzer] Please improve error message for enum constructor tear-off

[sgrekhov]

The code below produces an error but the error message reported by the analyzer is unclear.

enum E<T> {
  e0.id(1);

  final int v;
  const E.id(this.v);
}

main() {
  print(E.id); // Analyzer: Generative enum constructors can only be used as targets of redirection. Try using an enum value, or factory constructor. • invalid_reference_to_generative_enum_constructor
}

An error message reported by CFE is much clearer. It is "Error: Enum constructors can't be torn off.". Please update the analyzer's error message for enum constructor tear-off.

[lrhn]

Or at least: "Generative enum constructors can't be torn off". Factories can.

(Generative constructors of enum declarations are like generative constructors of abstract classes - you can't instantiate the class, so we won't give you a function which would do that.)

[FMorschel]

I'll take a look at this one

[FMorschel]

Here is the CL https://dart-review.googlesource.com/c/sdk/+/453360