compiletest: Support revisions in debuginfo (read: debugger) tests
And start using revisions in `tests/debuginfo/macro-stepping.rs` to prevent regressing both with and without `SingleUseConsts` MIR pass.
I recommend commit-by-commit review.
## ~TODO~
- [x] Verify this more carefully.
- [x] Possibly do some preparatory PRs before taking this PR out of draft.
- [x] Rebase on https://github.com/rust-lang/rust/pull/150205 once merged so we don't have to add another "`+ 1`".
## CC
CC ``@Zalathar`` since you might have opinions about that I expose a helper function to reduce duplication
CC ``@saethlin`` since this is what we will use for `tests/debuginfo/basic-stepping.rs` in https://github.com/rust-lang/rust/pull/147426 (in the same way I use it in `tests/debuginfo/macro-stepping.rs` here)
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