Auto merge of #150540 - JonathanBrouwer:incremental_test, r=cjgillot

Also hash spans inside the same file as relative (V2)

Hashes spans relatively to their parent, even if they are not contained inside their parent.

Fixes rust-lang/rust#150400

Closes rust-lang/rust#143882, as this is a successor PR
This PR is very closely based on that PR with a few minor changes, so to give proper credit I made @cjgillot coauthor of the commit.

Author: rust-bors[bot]