A STUDY TO EVALUATE THE EFFICACY AND SAFETY OF TRASTUZUMAB EMTANSINE IN COMBINATION WITH ATEZOLIZUMAB OR ATEZOLIZUMAB-PLACEBO IN PARTICIPANTS WITH HUMAN EPIDERMAL GROWTH FACTOR-2 (HER2) POSITIVE LOCALLY ADVANCED OR METASTATIC BREAST CANCER (BC) WHO RECEIVED PRIOR TRASTUZUMAB AND TAXANE BASED THERAPY: