Improve comments handling in couple of auto-corrections

[Darhazer]

I learned the hard way that the comments_before_line won't stop until the very first line in the processed file, and that it doesn't care whether the comments begin their own line or not. So I replaced it in the 2 cops that use it.

In one of them (that uses the CommentsHelp mixin) the code already tried to limit the damage by looking for consecutive lines, so it would only break if there is a node with inline comment and missing separating line.

The other one however would completely mess the comments, bringing all of the unrelated one to the new position, so I added spec for that case. It also fixes #9233

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

Looks good! Thanks!

[koic]

Thank you @Darhazer!