Add LAUNCHER_FOLDER_LABEL_CHANGED events for folder label updates.

Sample Logs for all update combinations: https://docs.google.com/document/d/1CBP2yTcXdFhPdNG5ZmWFKSgd8mDbMevY-akVlUXPLDo/edit#bookmark=id.7y1p8n2dz8ge

Bug: 155410872
Bug: 152978018
Change-Id: I296b124b16aa07878f2cf7b74ab91f13b8e6cfbf