EliciationCapability breaking change

[stephentoub]

With 06-18, there wasn't form vs url, so there weren't any members on ElicitationCapability. To opt-in to elicitation then, you'd just do:

Elicitation = new()

Now that there's form vs url, you need to do:

Elicitation = new()
{
    Form = new(),
}

and ElicitAsync will throw an exception if you don't add that Form = new(), even when 06-18 was negotiated.

Is that break by design?

cc: @halter73