Merge changes from topic "updatable-pi"

* changes:
  Testing replacement of IPackageDeleteObserver2
  Remove dependency on IPackageDeleteObserver2
  Remove dependency of on IPackageDeleteObserver
  Replace hidden APIs with new SystemAPIs
  Replace hidden APIs with their publicly avaiable variants
  AlertController cleanup
  Copying out AlertController and its relevant resources
  Expose new APIs required by Package Installer.