G1: Move Root Region Scan Waiting outside collection in logs

The `Root Region Scan Waiting` phase is printed inside `G1GCPhaseTimes::print_pre_evacuate_collection_set`. However, in `G1YoungCollector::collect`, `wait_for_root_region_scanning` is called before collection-start, i.e. `record_young_collection_start/pre_evacuate_collection_set`. Therefore, `Root Region Scan Waiting` should be printed earlier to match the actual order.