Clear indexing before adding all Slices

Before we index, add a call to clear indexed data before
indexing again. It's an optional call.

Fixes: 80065409
Test: robotests

Change-Id: Iddb0ce02c50d84b51fbf6fc2be0bdc9aa1f5987a

tests/robotests/src/com/android/settings/search/DeviceIndexUpdateJobServiceTest.java

@@ -124,6 +124,7 @@ public class DeviceIndexUpdateJobServiceTest {
 
         DeviceIndexFeatureProvider indexFeatureProvider = FakeFeatureFactory.getFactory(mActivity)
                 .getDeviceIndexFeatureProvider();
+        verify(indexFeatureProvider).clearIndex(any());
         verify(indexFeatureProvider, times(1)).index(any(), any(), any(), any(), any());
     }