Inlines bodies of playlist_get_custom_order, playlist_has_custom_order,
and playlist_get_tracks_with_local_copies from library/commands.rs
directly into the v2 wrappers in commands_v2/playlists.rs, mapping
LibraryError to RuntimeError::Internal as needed.
Deletes the corresponding legacy #[tauri::command] definitions and
removes their re-exports from library/mod.rs.
Step 8 of legacy cleanup, group F.
cc
vicrodh
7d18e6d3a8