FontPropertyBuilder should derive std::clone::Clone

[zacps]

If you want to select a number of fonts of the same family this lets you write:

let regularFont = system_fonts::FontPropertyBuilder::new().family("Noto Sans");
let italicFont = regularFont.clone().italic();

rather than:

let regularFont = system_fonts::FontPropertyBuilder::new().family("Noto Sans");
let italicFont = system_fonts::FontPropertyBuilder::new().family("Noto Sans").italic();