Add test for phrase search with stop words

Originally written by ManyTheFish here:
https://gist.github.com/ManyTheFish/f840e37cb2d2e029ce05396b4d540762

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

milli/tests/search/mod.rs

@@ -18,6 +18,7 @@ mod filters;
 mod query_criteria;
 mod sort;
 mod typo_tolerance;
+mod phrase_search;
 
 pub const TEST_QUERY: &'static str = "hello world america";