Currently if task_manager::task::impl::abort preempts before children are recursively aborted and then the task gets unregistered, we hit use after free since abort uses children vector which is no longer alive.
Modify abort method so that it goes over all tasks in task manager and aborts those with the given parent.
Fixes: https://github.com/scylladb/scylladb/issues/19304.
Requires backport to all versions containing task manager
(cherry picked from commit 3463f495b1)
(cherry picked from commit 50cb797d95)
Refs https://github.com/scylladb/scylladb/pull/19305Closesscylladb/scylladb#19437
* github.com:scylladb/scylladb:
test: add test for abort while a task is being unregistered
tasks: fix tasks abort
fa644c6269