Start to support adding shortcuts.

...olicyimpl/dictionary/shortcut/ver4_shortcut_list_policy.h

...olicyimpl/dictionary/structure/pt_common/pt_node_writer.h

...ry/structure/v3/dynamic_patricia_trie_updating_helper.cpp

...nary/structure/v3/dynamic_patricia_trie_updating_helper.h

...l/dictionary/structure/v4/content/shortcut_dict_content.h

...ictionary/structure/v4/ver4_patricia_trie_node_writer.cpp

.../dictionary/structure/v4/ver4_patricia_trie_node_writer.h

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

...cyimpl/dictionary/utils/buffer_with_extendable_buffer.cpp

.../src/suggest/policyimpl/dictionary/utils/sparse_table.cpp

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