Define KEY as TRANS in a Quail map MAP.
If Optional 4th arg APPEND is non-nil, TRANS is appended to the
current translations for KEY instead of replacing them.
Optional 5th arg DECODE-MAP is a Quail decode map.
Optional 6th arg PROPS is a property list annotating TRANS. See the
function `quail-define-rules' for the detail.
(fn KEY TRANS MAP &optional APPEND DECODE-MAP PROPS)