Function emit_image_xobject 

pub(crate) fn emit_image_xobject(
    pdf: &mut Pdf,
    id: Ref,
    handle: &ImageHandle,
    compressed: &[u8],
)

Emit one Image XObject (/Subtype /Image) for handle at id. compressed is the zlib-compressed pixel stream produced by flate_compress; passed in pre-compressed so the caller can hold onto the bytes for byte-stability assertions in tests.