function Identifier$1(params) {
    Transform.call(this, 0, params);
  }
Adds a unique identifier to all added tuples.
This transform creates a new signal that serves as an id counter.
As a result, the id counter is shared across all instances of this
transform, generating unique ids across multiple data streams. In
addition, this signal value can be included in a snapshot of the
dataflow state, enabling correct resumption of id allocation.
@constructor
@param {object} params - The parameters for this operator.
@param {string} params.as - The field name for the generated identifier.