Use PrevWordsInfo to add/remove n(bi)-gram in native code.

...ve/jni/com_android_inputmethod_latin_BinaryDictionary.cpp

native/jni/src/suggest/core/dicnode/dic_node.h

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

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

...ni/src/suggest/core/dictionary/property/bigram_property.h

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

native/jni/src/suggest/core/session/dic_traverse_session.cpp

native/jni/src/suggest/core/session/prev_words_info.h

...ary/structure/backward/v401/ver4_patricia_trie_policy.cpp

...onary/structure/backward/v401/ver4_patricia_trie_policy.h

...cture/dictionary_structure_with_buffer_policy_factory.cpp

...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