Replace all uses of lagi_wxString with to_wx

aegisub/src/ass_attachment.cpp

aegisub/src/ass_dialogue.cpp

aegisub/src/ass_file.cpp

aegisub/src/audio_controller.cpp

aegisub/src/audio_player_alsa.cpp

aegisub/src/audio_player_oss.cpp

aegisub/src/audio_player_portaudio.cpp

aegisub/src/audio_provider_ffmpegsource.cpp

aegisub/src/audio_provider_hd.cpp

aegisub/src/audio_provider_pcm.cpp

aegisub/src/audio_provider_ram.cpp

aegisub/src/auto4_base.cpp

aegisub/src/auto4_lua.cpp

aegisub/src/auto4_lua_dialog.cpp

aegisub/src/auto4_lua_scriptreader.cpp

aegisub/src/base_grid.cpp

aegisub/src/command/app.cpp

aegisub/src/command/audio.cpp

aegisub/src/command/command.cpp

aegisub/src/command/keyframe.cpp