feat: add support for respecting $XDG_DATA_HOME and $AUTOJUMP_DARWIN_XDG on macOS

• respecting a new env $AUTOJUMP_DARWIN_XDG: If $XDG_DATA_HOME is set, use it as the autojump's data home; else if the OS is macOS and $AUTOJUMP_DARWIN_XDG is false, use ~/Library (for compatibility); otherwise, use XDG's fallback path (i.e., ~/.local/share).
• remove migrate_osx_xdg_data() in autojump_data.py
• related issue: #447 (closed)