Migrate to Android Testing Support Lib (part 2/N)

This CL converts tests under com.android.inputmethod.compat to
Android Testing Support Library.

Bug: 110805255
Test: verified as follows. No new test failures.
        tapas adb LatinIME LatinIMETests arm64 userdebug && \
        DISABLE_PROGUARD=true make -j LatinIME && \
        adb install -r $OUT/system/app/LatinIME/LatinIME.apk && \
        atest LatinIMETests:com.android.inputmethod.compat
Change-Id: I6766447ca27f5cccdb1e9f7e751235daa04cc252