(#16791) Re-instate deprecated symbolize and symbolizehash!

The cherry-pick of commit a09df46f58187ad9ff0f599de47cd8c1e0a417eb to
remove the use of symbolize throughout the code base also removed the
symbolize method, as well as the symbolizehash! method. The cherry-pick
was needed so that the methods could be deprecated without puppet
issuing warnings from using them.

This commit puts the two methods back and also places a deprecation
warning in them.