Client app crashes if accessibility service uses invalid focus type.

1. If an accessibility service uses an invalid focus type argument
   when trying to find where focus is the queried application crashes.
   The same happens if the serivce calls focus search with an invalid
   derection. While we need the argument check in the controller that
   runs in the app process the accessibility service has to be the
   palace where an exception is thown for the invalid argument so
   the developer can fix his code.:

bug:6508797

Change-Id: Ib0d74f374fa60ee8fd6117f11c23af34f6c26ad3