optimize `_updateLocalClasses` in Inspector Service

_updateLocalClasses fetches each of the objects individually. This causes a performance bottleneck on pub root directory change.
If this class ends up being needed, the we will need to find a call that batches the request, to avoid overloading the vm with rpc calls.

**NOTE:** `isLocalClass` may not be hooked up to the fronted properly yet. So doing this optimization may not be needed until that is accomplished