202: Add field id word count docids database r=Kerollmops a=LegendreM
This PR introduces a new database, `field_id_word_count_docids`, that maps the number of words in an attribute with a list of document ids. This relation is limited to attributes that contain less than 11 words.
This database is used by the exactness criterion to know if a document has an attribute that contains exactly the query without any additional word.
Fix#165Fix#196
Related to [specifications:#36](https://github.com/meilisearch/specifications/pull/36)
Co-authored-by: many <maxime@meilisearch.com>
Co-authored-by: Many <legendre.maxime.isn@gmail.com>
