[DAG] Fold extract_subvector(insert_subvector(x,y,c1),c2) -->...

[DAG] Fold extract_subvector(insert_subvector(x,y,c1),c2) --> extract_subvector(y,c2-c1) (#87925) (REAPPLIED)

If the extract_subvector is cheap, attempt to extract directly from an inserted subvector

Reapplied with a check to ensure we only attempt this for fixed vectors