[roll] Roll fuchsia [starnix][kernel] Deliver zombie tracee notifications on exit

Previously, when a tracer thread group exited, it would release its
zombie tracees. This resulted in either lost zombie notifications, as
the zombies were never forwarded to their parents, or leaked zombies,
resulting in kernel panic.

This change closes this gap by ensuring that:

  1. Every zombie tracee is detached on tracer exit.
  2. Every detached zombie is delivered to its parent.

The ZombieNotification type is introduced to encapsulate the process of
detaching a zombie tracee, generating a parent notification, and
delivering that notification in a safe context. Notification production
and delivery are split into two distinct steps to avoid deadlock.

Several concurrent exit races are closed, too.

Original-Original-Bug: 527225621
Multiply: ptrace_test
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1688177
Original-Original-Revision: af60521df1bbab50acb6e7aa937b3f47d5907f07
GitOrigin-RevId: a519066f7aa18995707a61220d6fe06b38058512
Change-Id: I0ac5592ca59d1e8e900c3c9bda5644909633a7b3
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1695614
Cr-Commit-Position: refs/heads/main@{#196234}