Require `-language=english_extra` to produce the complete version of
the new JMdict dictionary file.
If and when we determine that the all the new features are ready to be
included the dictionary by default, we can remove this logic.
This commit ensures that terms are grouped among their entries of
origin and displayed in correct sequential order in Yomichan's default
result grouping mode, "Group term-reading pairs."
If a headword appears in multiple entries, then each entry needs a
corresponding "forms" term in the output dictionary.
For example, 軽卒 is the only headword in entry 2275730, but 軽卒 also
appears as an irregular form in entry 1252910. If a "forms" term is
not included for the former entry, then it will appear that 軽卒 is
irregular for all senses in the output dictionary.
This allows a user to install the English version and another version
without cluttering their setup with duplicated information.
If a user doesn't want to use the English version, they can get the
"search" and "forms" terms by installing the separate jmdict_forms
file.
