Move files under bigram/shortcut to under structure.

native/jni/NativeFileList.mk

...ructure/pt_common/bigram/bigram_list_read_write_utils.cpp

...structure/pt_common/bigram/bigram_list_read_write_utils.h

...ucture/pt_common/shortcut/shortcut_list_reading_utils.cpp

...tructure/pt_common/shortcut/shortcut_list_reading_utils.h

...yimpl/dictionary/structure/v2/bigram/bigram_list_policy.h

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

...l/dictionary/structure/v2/shortcut/shortcut_list_policy.h

...ictionary/structure/v4/bigram/ver4_bigram_list_policy.cpp

.../dictionary/structure/v4/bigram/ver4_bigram_list_policy.h

...tionary/structure/v4/shortcut/ver4_shortcut_list_policy.h

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

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

...ionary/structure/v4/ver4_patricia_trie_writing_helper.cpp