Various changes following Simon’s review:
Base class always calculates DocFreq now - removed boolean flag that made this optional.
Simplified logic handling where different codecs used some with TTF some without
Option to control totalTermFreq calculation now controlled using existing DocsEnum#flag setting rather than new boolean.
Changed single DocsEnum iteration-heavy loop to a choice of 2 loops with appropriate inner logic depending on mode.
Tidied resource tearDown in FreqTermsEnumTests