fix: Don't move comments while splitting delimiters

[cobaltt7]

Description

Resolves #4220. Black moved the + at the end of the line to the start of the next line, then unintentionally moved any comments as well. This could cause comments to be merged. To fix this, I stopped Black from moving any comments with the delimiter. It only crashed when merging type: ignore comments, but I think it makes sense to keep all comments on their original line instead of following the delimiter. This does not break the stability policy since already-Blackened code will not change.

Depends on #4257 for lint to succeed.

Checklist - did you ...

• [y] Add an entry in CHANGES.md if necessary?
• [y] Add / update tests if necessary?
• [-] Add new / update outdated documentation?

[cobaltt7]

Test failures and diff-shades crash are caused by

 bad_split3 = (
-    "What if we have inline comments on "  # First Comment
-    "each line of a bad split? In that "  # Second Comment
-    "case, we should just leave it alone."  # Third Comment
+    "What if we have inline comments on "  # First Comment  # Second Comment  # Third Comment
+    "each line of a bad split? In that "
+    "case, we should just leave it alone."
 )

[github-actions]

diff-shades reports zero changes comparing this PR (8e1dfd3) to main (0f18001).

---

What is this? | Workflow run | diff-shades documentation

[cobaltt7]

I have extracted the unrelated refactorings to #4257 for ease of review. That needs to be merged before lint passes on this PR.

[JelleZijlstra]

Thank you!