fts_phrase_or_proximity_search() is quadratic instead of linear

MySQL 8.0.43 includes the change Bug #37682648 InnoDB FTS slow in phrase search due to inefficient matching of doc_id. If we ignore all the boilerplate changes and renaming of two functions, it boils down to revising fts_phrase_or_proximity_search() in such a way that we remember where a previous search left off, so that we will avoid restarting the search from the beginning.

We might want to take this further and introduce a template parameter for the query mode, so that each template expansion handles only FTS_PHRASE or FTS_PROXIMITY but not both. I wouldn’t introduce any Vector_wrapper but instead consider extending or replacing the ib_vector_t if needed.