Lucene should have an entirely memory resident term dictionary

FST based TermDictionary has been a great improvement yet it still uses a delta codec file for scanning to terms. Some environments have enough memory available to keep the entire FST based term dict in memory. We should add a TermDictionary implementation that encodes all needed information for each term into the FST (custom fst.Output) and builds a FST from the entire term not just the delta.