constructor() {
    super('__moduleName');
    this.usesModuleName = false;
  }
Replaces __moduleName with $__moduleContext.id

This allows code to use the __moduleName temporary syntax to reference 
the current module name for relative importing via System.import('./x', __moduleName)
In the future this will be deprecated and $__moduleContext extended in the implementation
to support any contextual metadata and loading features determined in the spec.