Fix lint warnings under core/tests/coretests/src/android/view/inputmethod/

This is a mechanical refactoring.  There should be no change regarding
what's asserted in IME tests implemented in FrameworksCoreTests.

Bug: 171827834
Test: atest FrameworksCoreTests:android.view.inputmethod
Test: prebuilts/checkstyle/checkstyle.py \
        -f frameworks/base/core/tests/coretests/src/android/view/inputmethod/ \
        | grep .java:
Change-Id: I9daa0cc76e90715a6c77526096af80660af0a9b4