Add a jni method to iterate words in a dictionary.

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

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

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

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

...est/core/policy/dictionary_structure_with_buffer_policy.h

...policyimpl/dictionary/structure/v2/patricia_trie_policy.h

...mpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp

...yimpl/dictionary/structure/v4/ver4_patricia_trie_policy.h