Font sorting through fontconfig support

There’s an issue for it: Slow startup on Linux due to font loading of **all** the system fonts in `/usr/share/fonts` · Issue #2455 · iced-rs/iced · GitHub

I think supporting fontconfig is necessary, because I’d like to display emojis and Chinese characters on different platforms, but guessing what fonts the users have or bring a new font to the users doesn’t seem to be a good idea.

In addition, by now only the text element supports the Advanced shaping and it doesn’t seem to be enough for displaying different characters.

I’d like to know why iced chose to processing fonts itself. Any thoughts on this?