Rollup merge of #126454 - cuviper:deterministic-bump, r=Kobzol

bump-stage0: use IndexMap for determinism

When it used `HashMap`, `bump-stage0` would change `src/stage0` every
time it ran, whereas `IndexMap` will keep insertion order -- matching
the manifest file.

I included an actual bump here mainly to reset the order, but that did
update to a new rustfmt nightly too.

Author: matthiaskrgr