Support migration/dump of Beginning-of-Sentence entries.

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

.../com/android/inputmethod/latin/makedict/WordProperty.java

.../android/inputmethod/latin/utils/CombinedFormatUtils.java

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

...ni/src/suggest/core/dictionary/property/word_property.cpp

native/jni/src/utils/char_utils.h

native/jni/src/utils/jni_data_utils.h

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

...tmethod/latin/makedict/BinaryDictDecoderEncoderTests.java