Adding in Clear Credential Implementation This will add on the ability to clear credentials to the play auth module implementation. Relnote: """Added more generic Void? type rather than Void across java and kotlin for clearing credentials, specifically for use in the callback for clear credentials""" Bug: 258061894 Test: WIP JUnit Tests, design concept only for now (builds fine) Change-Id: If61f4f3c98e4e13129ca722eee9e953306f19e56