feat!: migrate FTS from tantivy to lance-index (#1483)

Lance now supports FTS, so add it into lancedb Python, TypeScript and
Rust SDKs.

For Python, we still use tantivy based FTS by default because the lance
FTS index now misses some features of tantivy.

For Python:
- Support to create lance based FTS index
- Support to specify columns for full text search (only available for
lance based FTS index)

For TypeScript:
- Change the search method so that it can accept both string and vector
- Support full text search

For Rust
- Support full text search

The others:
- Update the FTS doc

BREAKING CHANGE: 
- for Python, this renames the attached score column of FTS from "score"
to "_score", this could be a breaking change for users that rely the
scores

---------

Signed-off-by: BubbleCal <bubble-cal@outlook.com>

nodejs/src/index.rs

@@ -14,7 +14,7 @@
 
 use std::sync::Mutex;
 
-use lancedb::index::scalar::BTreeIndexBuilder;
+use lancedb::index::scalar::{BTreeIndexBuilder, FtsIndexBuilder};
 use lancedb::index::vector::IvfPqIndexBuilder;
 use lancedb::index::Index as LanceDbIndex;
 use napi_derive::napi;
@@ -76,4 +76,11 @@ impl Index {
             inner: Mutex::new(Some(LanceDbIndex::BTree(BTreeIndexBuilder::default()))),
         }
     }
+
+    #[napi(factory)]
+    pub fn fts() -> Self {
+        Self {
+            inner: Mutex::new(Some(LanceDbIndex::FTS(FtsIndexBuilder::default()))),
+        }
+    }
 }

nodejs/src/query.rs

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use lancedb::index::scalar::FullTextSearchQuery;
 use lancedb::query::ExecutableQuery;
 use lancedb::query::Query as LanceDbQuery;
 use lancedb::query::QueryBase;
@@ -42,6 +43,12 @@ impl Query {
         self.inner = self.inner.clone().only_if(predicate);
     }
 
+    #[napi]
+    pub fn full_text_search(&mut self, query: String, columns: Option<Vec<String>>) {
+        let query = FullTextSearchQuery::new(query).columns(columns);
+        self.inner = self.inner.clone().full_text_search(query);
+    }
+
     #[napi]
     pub fn select(&mut self, columns: Vec<(String, String)>) {
         self.inner = self.inner.clone().select(Select::dynamic(&columns));
@@ -138,6 +145,12 @@ impl VectorQuery {
         self.inner = self.inner.clone().only_if(predicate);
     }
 
+    #[napi]
+    pub fn full_text_search(&mut self, query: String, columns: Option<Vec<String>>) {
+        let query = FullTextSearchQuery::new(query).columns(columns);
+        self.inner = self.inner.clone().full_text_search(query);
+    }
+
     #[napi]
     pub fn select(&mut self, columns: Vec<(String, String)>) {
         self.inner = self.inner.clone().select(Select::dynamic(&columns));