WaiterQueueNodes as used by JS synchronization primitives are per-main
thread, and external pointer handles to those nodes are 1-1. That
1-1-ness is captured by each main thread Isolate having a
waiter_queue_node_external_pointer_ field.

The current logic is incorrect on unlock paths as the Isolate that
requested the unlock can point its own
waiter_queue_node_external_pointer_ to another Isolate's
WaiterQueueNode. This CL fixes this by having each WaiterQueueNode hold onto its own external pointer handle.

This CL also fixes an embarrassing bug where the WaiterQueueNode was not correctly dequeued on timeout.

Bug: v8:13189, v8:12547
Change-Id: I8db16ae6d653d2e71989ad003faae20fcee06a25
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3832298
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82601}