Function decrypt 

fn decrypt(
    bytes: impl Iterator<Item = u8>,
    seed: u32,
) -> impl Iterator<Item = u8>

Returns an iterator yielding the decrypted bytes.

See https://gitlab.freedesktop.org/freetype/freetype/-/blob/80a507a6b8e3d2906ad2c8ba69329bd2fb2a85ef/src/psaux/psconv.c#L557