[roll] Roll fuchsia [starnix] Refactor mutable state of ThreadGroup

ThreadGroup contains 10 different locks. This makes correctly handling
lock ordering next to impossible. This CL refactors ThreadGroup to
extract the mutable states inside a single internal struct protected by
a RwLock.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/671567
Original-Revision: f26616b682847abbe202d88cb5ae0a4cf4c55190
GitOrigin-RevId: 2de221f800681d903bcfa8b00b8676dca309fa16
Change-Id: Ic79b31ac1c5e73d720a80d78e8e7182e91b9a0ee
diff --git a/stem b/stem
index 6f2ae36..4772b9c 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="a784cab03597a6e88da9bb549f4940dd942b9967"/>
+             revision="f26616b682847abbe202d88cb5ae0a4cf4c55190"/>
   </projects>
   <hooks>
     <hook name="install-environment"