name 15 th16 MainMenu funcs

[Renko6626]

Label 15 previously-unnamed functions in the TH16 v1.00a main menu
(ZUN's TitleInf), and replace the sub_451560 placeholder.

From Ghidra decompilation + cross-checks:

• state machine: change_menu, destructor, delete_singleton, do_help_manual
• options / key config draw helpers
• replay: load_replay_files_thread (was sub_451560_start_of_a_thread__rpy_related),
  draw_spellcard_score_rows
• spell practice: update_spellcard_list, update_selection_anm, is_accessible
• text helpers: text_skip_line, text_read_line_into_buf