False positive prefer_const_constructors_in_immutables with enum comparison in assert

[a14n]

The following code triggers prefer_const_constructors_in_immutables on A constructor but it shouldn't as enum comparisons are not yet allowed in asserts.

enum E { a, b }
@immutable
class A {
  A([E e = E.b]) : assert(e != E.a);  // LINT is here but it shouldn't trigger
}

It looks related to const evaluation as there's no analyzer error on the constructor if we make the constructor const though there's an error on the constructor invocation.

enum E { a, b }
@immutable
class A {
  const A([E e = E.b]) : assert(e != E.a); // no diagnostic but there should be an `invalid_constant` error for `e != E.a`
}
void main() {
  const A(); // const_evaluation_throws_exception
}

Filed also #45441

/cc @scheglov @bwilkerson