Support AS clause in GRANT statement

Hi, It might be duplicate for DBZ-3978 but it seems like it is not fixed in 1.6.2.Final

DDL statement couldn't be parsed. Please open a Jira issue with the statement 'GRANT SELECT ON . TO 'username'@'cloudsqlproxy~10.%.%.%' AS 'dbaname'@'cloudsqlproxy~10.%.%.%' WITH ROLE 'cloudsqlsuperuser'@'%''
mismatched input 'AS' expecting {<EOF>, '--'}