Migrate IME related tests to JUnit4

This CL cleans up remaining use of InstrumentationTestCase from
IME-related FrameworksCoreTests as it is already deprecated in favor of
testing-support-library.

There should be no behavior change in tests and their expectations.

Fixes: 70514197
Test: atest FrameworksCoreTests:com.android.internal.inputmethod.InputMethodSubtypeSwitchingControllerTest
Test: atest FrameworksCoreTests:com.android.internal.inputmethod.InputMethodUtilsTest
Test: atest FrameworksCoreTests:com.android.internal.inputmethod.LocaleUtilsTest
Test: atest FrameworksCoreTests:android.view.inputmethod.CursorAnchorInfoTest
Test: atest FrameworksCoreTests:android.view.inputmethod.InputMethodSubtypeArrayTest
Test: atest FrameworksCoreTests:android.view.inputmethod.InputMethodSubtypeTest
Test: atest FrameworksCoreTests:android.view.inputmethod.SparseRectFArrayTest
Change-Id: I28f073aacb6f77c62bd186c37cbdb5719475d4ba