Fix and refactor syntactic loop unrolling

[sim642]

While working on fixing loop heads in YAML witnesses, I wanted to finally implement a cleaner fix to #1225 than #1248 by recording somewhere which statements came from loop unrolling.
To do this, I wanted to refactor things a bit and added cram tests to make sure I don't accidentally break anything. But I also discovered that continues are mishandled in loop unrolling from #563.

Changes

1. Add cram tests for loop unrolling.
2. Mark unrolled loop head labels as not originating from input code but transformations, like CIL does.
3. Fix continue in loop unrolling. Due to (double) refs, there was undesirable sharing which caused all unrolled iterations to jump directly to the unrolled part, not to the next unrolled iteration as intended. Imperative programming is again dangerous.
4. Add option dbg.justcil-printer to allow cram testing justcil output without clutter from line directives and builtin declarations.
5. Remove excessive blocks from loop unrolling output.
6. Remove goblint_array_domain attribute from non-array variables.

[michael-schwarz]

Nice catch! Do you think you can also craft an example where the better handling of continue means that an assertion that was previously failing now succeeds?

[sim642]

There's now a test that fails on master.