A resolver is an object providing the ability to resolve a promise.
A resolver does not allow retrieving the reference to which a promise has been resolved; in E (but not in ref_send), a resolver allows observing whether resolution has occurred.
Resolves the promise to resolution, or throws if it is already resolved.
Equivalent to resolveRace(Ref.broken(problem)).
Returns whether the promise is already resolved.
The specification for this message has not been written.