Move IME related unit tests under core/tests/coretests/.

This CL moves existing (non-CTS) unit tests used for input
method under core/tests/coretests/ to reduce the maintenance
cost.

Although some package names and import lines are updated
to be consistent with new file locations, test cases are
are kept to be the same.

Change-Id: I4efce90b232458212ac48292dc01b812a9e851e5