from Json To RVariable
  Converts a JSON string representation into an instance of RVariableIfc. The method parses the JSON string, maps it to an RVData object, and then transforms it into an implementation of RVariableIfc using the asRVariable method.
Return
An instance of RVariableIfc created from the provided JSON string.
Parameters
json String
The JSON string to be parsed, containing the necessary data to construct a random variable.