Fix lint warnings in InputMethodSubtypeSwitchingController

This is a mechanical refactoring.  There should be no behavior change.

Bug: 171827834
Test: atest -mc FrameworksServicesTests:InputMethodSubtypeSwitchingControllerTest
Test: prebuilts/checkstyle/checkstyle.py -f \
         frameworks/base/services/core/java/com/android/server/inputmethod/InputMethodSubtypeSwitchingController.java
Change-Id: I12e922bf4b0b4f4e8dfe16a1d71b22b29b7fabc5