Function shift_footnote_refs_for_insert 

pub fn shift_footnote_refs_for_insert(
    notes: &mut [FootnoteRefAnchor],
    byte_offset: u32,
    inserted_bytes: u32,
)

Apply an “insert” shift to a block’s image anchors. Anchors at or past the offset move forward by inserted_bytes. Apply an “insert” mutation to a block’s footnote references — the rule shift_images_for_insert applies, for the same reason.