Function font_decode 

pub fn font_decode(
    code: i32,
    encoding_opt: Option<&str>,
    font_opt: Option<Rc<Font>>,
) -> (Option<char>, Option<Rc<Font>>)

Decode a codepoint using the fontmap for a given font and/or encoding (Perl: FontDecode). Returns the decoded glyph (if any) and the possibly-adjusted font.