Use trigrams for personalization dict.

java/src/com/android/inputmethod/latin/BinaryDictionary.java

.../com/android/inputmethod/latin/DictionaryFacilitator.java

...android/inputmethod/latin/ExpandableBinaryDictionary.java

.../latin/PersonalizationHelperForDictionaryFacilitator.java

...tmethod/latin/utils/WordInputEventForPersonalization.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

native/jni/src/utils/jni_data_utils.h

...roid/inputmethod/latin/BinaryDictionaryDecayingTests.java

.../com/android/inputmethod/latin/BinaryDictionaryTests.java

...latin/personalization/PersonalizationDictionaryTests.java