Merge #598

598: Matching query terms policy r=Kerollmops a=ManyTheFish

## Summary

Implement several optional words strategy.

## Content

Replace `optional_words` boolean with an enum containing several term matching strategies:
```rust
pub enum TermsMatchingStrategy {
    // remove last word first
    Last,
    // remove first word first
    First,
    // remove more frequent word first
    Frequency,
    // remove smallest word first
    Size,
    // only one of the word is mandatory
    Any,
    // all words are mandatory
    All,
}
```

All strategies implemented during the prototype are kept, but only `Last` and `All` will be published by Meilisearch in the `v0.29.0` release.

## Related

spec: https://github.com/meilisearch/specifications/pull/173
prototype discussion: https://github.com/meilisearch/meilisearch/discussions/2639#discussioncomment-3447699


Co-authored-by: ManyTheFish <many@meilisearch.com>

benchmarks/benches/utils.rs

@@ -11,7 +11,7 @@ use milli::heed::EnvOpenOptions;
 use milli::update::{
     IndexDocuments, IndexDocumentsConfig, IndexDocumentsMethod, IndexerConfig, Settings,
 };
-use milli::{Filter, Index, Object};
+use milli::{Filter, Index, Object, TermsMatchingStrategy};
 use serde_json::Value;
 
 pub struct Conf<'a> {
@@ -119,7 +119,7 @@ pub fn run_benches(c: &mut criterion::Criterion, confs: &[Conf]) {
                 b.iter(|| {
                     let rtxn = index.read_txn().unwrap();
                     let mut search = index.search(&rtxn);
-                    search.query(query).optional_words(conf.optional_words);
+                    search.query(query).terms_matching_strategy(TermsMatchingStrategy::default());
                     if let Some(filter) = conf.filter {
                         let filter = Filter::from_str(filter).unwrap().unwrap();
                         search.filter(filter);