Add missing Korean support

Some configuration is missing `korean` features and
add a test case in `milli/src/search/mod.rs`.

milli/src/search/mod.rs

@@ -336,4 +336,28 @@ mod test {
 
         assert_eq!(documents_ids, vec![1]);
     }
+
+    #[cfg(feature = "korean")]
+    #[test]
+    fn test_hangul_language_detection() {
+        use crate::index::tests::TempIndex;
+
+        let index = TempIndex::new();
+
+        index
+            .add_documents(documents!([
+                { "id": 0, "title": "The quick (\"brown\") fox can't jump 32.3 feet, right? Brr, it's 29.3°F!" },
+                { "id": 1, "title": "김밥먹을래。" },
+                { "id": 2, "title": "הַשּׁוּעָל הַמָּהִיר (״הַחוּם״) לֹא יָכוֹל לִקְפֹּץ 9.94 מֶטְרִים, נָכוֹן? ברר, 1.5°C- בַּחוּץ!" }
+            ]))
+            .unwrap();
+
+        let txn = index.write_txn().unwrap();
+        let mut search = Search::new(&txn, &index);
+
+        search.query("김밥");
+        let SearchResult { documents_ids, .. } = search.execute().unwrap();
+
+        assert_eq!(documents_ids, vec![1]);
+    }
 }