[roll] Roll fuchsia [starnix] Fix lock ordering in controlling terminal disassociation

The `disassociate_controlling_terminal` function iterates through thread
groups in the foreground process group and acquires their
`ThreadGroupMutableState` locks. Previously, it was called while already
holding the `ThreadGroupMutableState` lock of the exiting session
leader. This caused a lock order violation.

To enforce the correct lock order, `disassociate_controlling_terminal`
must be called after dropping any `ThreadGroupMutableState` lock.

This change introduces a `#[must_use]` `SessionDisassociation` struct
returned by `leave_process_group` and `set_process_group`. Callers
(like `ThreadGroup::remove`, `setpgid`, and `setsid`) must explicitly
call `.disassociate_controlling_terminal()` on the returned value
after dropping the `ThreadGroupMutableState` lock, ensuring the fix
is safe and cannot be forgotten.

Original-Original-Fixed: b/529617819
Original-Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1686794
Original-Original-Revision: 796b4c6ca888d87b4b6e8fb5d34fa38649c4a1e2
GitOrigin-RevId: 8991472929e8626775555807c3319539a3f01f00
Change-Id: I10d062aa48337712a149805cd674f3e16b8b0cbc
Reviewed-on: https://fuchsia-review.googlesource.com/c/integration/+/1686505
Cr-Commit-Position: refs/heads/main@{#195881}