Extend jni interface to get bigrams in WordProperty.

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

...src/com/android/inputmethod/latin/utils/WordProperty.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

native/jni/src/suggest/core/dictionary/word_property.cpp

native/jni/src/suggest/core/dictionary/word_property.h

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