Update benchmarking library code to work for IdMap index as well (#4093)

Summary:
Pull Request resolved: #4093

Update benchmarking library code to work for IdMap index as well by calling add_with_ids instead of add since ids are required for IDMap index

Reviewed By: gtwang01

Differential Revision: D67254267

fbshipit-source-id: 947a141edbdd7e44d33a297054869e3b932e3b89

benchs/bench_fw/index.py

@@ -677,6 +677,13 @@ def fetch_index(self):
                 lambda: add_preassigned(index_ivf, xbt, QI.ravel()),
                 once=True,
             )
+        elif isinstance(index, faiss.IndexIDMap):
+            _, t, _ = timer(
+                "add_with_ids",
+                lambda: index.add_with_ids(
+                    xb, np.arange(len(xb), dtype='int32')),
+                once=True,
+            )
         else:
             _, t, _ = timer(
                 "add",