Adds Module::GetStalledTopLevelAwaitMessage() API which searches for
modules that have no pending async dependencies but have not yet
resolved. An embedder may call this API when they are about to exit
to check if TLA evaluation has stalled and provide a better error
message.

Change-Id: I3b88802f70cc84c973551f13d73ef3e3d06f4027
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2341765
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81080}