Add a new API action for reading lexicon entries.
This is only responsible for asking an internal mechanism for the lexicon entry. Resolving if a Speechoid call is needed and performing that is owned by the result of T274504: Implement LexiconBase and LexiconLocalPersistency
This will be used by edit lexicon special page: T181269: ☂Create a special page for adding entries to the lexicon.