[Enhancement] Use "Author Sort" instead of "Author" in the folder structure

When adding a book whose "Author" or "Title" field use non-Latin characters, Calibre displays the original name in its GUI, but the folders in the filesystem are Romanised. This makes perfect sense, as there is seldom need to access the books via the filesystem, which in turn might not play nice with non-Latin characters.

The problem arises, in my experience, when adding Japanese books. Japanese is usually written via Chinese characters, which are Romanised by Calibre as if they were Hanyu Pinyin, i.e. using their Chinese pronunciation. This turns the filesystem folder name for both author and title into unreadable gibberish.

A partial solution to the above is changing Calibre's language to Japanese, but then the same issue (I imagine) arises for Chinese books.

The solution I would propose is to use "Sort Author" and "Sort Title" for the filesystem names: these are used for sorting alphabetically, thus they need to be Romanised to begin with.