peekValue
Call getValue without being observed.
    ObservationRecorder.peekValue(obj)
  
  .peekValue will call obj's @can.getValue symbol and return the result.  If it does not have that symbol,
obj will be returned.  Any calls to ObservationRecorder.add made will be ignored.
import {value, ObservationRecorder} from "can";
var num = value.with(3)
ObservationRecorder.peekValue(num) //-> 3