fn parse_fixed_dynamic(cursor: &mut Cursor<'_>) -> Result<(Fixed, i32), Error>
Parse a fixed point value with a dynamic scaling factor.
See https://gitlab.freedesktop.org/freetype/freetype/-/blob/f1cd6dbfa0c98f352b698448f40ac27e8fb3832e/src/cff/cffparse.c#L580