Better `const_with_non_constant_argument` message when argument is closure

[FMorschel]

Repro:

enum MyEnum {
  v(() {});
//  ^ const_with_non_constant_argument

  const MyEnum(Function f);
}

Message:

Arguments of a constant creation must be constant expressions.
Try making the argument a valid constant, or use 'new' to call the constructor.

We should probably suggest creating a static method, a const constructor or a top-level function.

CC @bwilkerson