[main] Rewrite rootrm in C++

[silverweed]

This PR introduces a C++ version of rootrm, replacing the python version.
The semantics are mostly the same, but there is a new -n flag to do a "dry run" (useful for testing).

Note that this doesn't currently fix #21090

Checklist:

• tested changes locally

[pcanal]

Thanks.

[github-actions]

Test Results

    22 files      22 suites   3d 5h 12m 46s ⏱️
 3 800 tests  3 795 ✅ 0 💤 5 ❌
75 582 runs  75 577 ✅ 0 💤 5 ❌

For more details on these failures, see this check.

Results for commit 469175b.

♻️ This comment has been updated with latest results.

[vepadulano]

Thanks, this is great! Just a few minor questions from my side.

[vepadulano]

Cool, thanks!