* Attempt 4: Prevent reparenting a block with itself (#38747)
* More concisely reparent, ensuring we don't go too shallow or too deep in this process. Fixes#38357
* More explicit reparenting, with a short circuit for a common case
* We need new_block to have a parent, otherwise we lose context with this approach
* Remove duplicate parent assignment
* Change callers of Block.copy to not use exclude_parent=True, when including the parent, exclude tasks
(cherry picked from commit f474195a3b)
* Add changelog for #38747
