Can't compare things against null in asserts in const constructors

[Hixie]

This fails in the analyzer with a CONST_EVAL_TYPE_BOOL_NUM_STRING:

class Test { }

class Foo {
  const Foo({
    this.test,
  }) : assert(test == null); // In constant expressions, operands of this operator must be of type 'bool', 'num', 'String' or 'null'.
  final Test test;
}

void main() { }

[lrhn]

Constant expression were changed in the specification for Dart 2 so that this should be allowed.
(The old "e1 == e2 is constant if" were updated to also say "or e1 or e2 is null").

[scheglov]

Fixed in https://dart-review.googlesource.com/c/sdk/+/71340