This is a reland of 11524453

Original change's description:
> [wasm] Test concurrent code emission
> 
> This extends the jump table stress test. Currently, we generate
> different thunks (on the main thread) and then concurrently update the
> jump table to jump to one of these thunks.
> With this CL, we also generate the thunks concurrently. So this also
> tests whether there is proper synchronization between code generation
> and executing it in another thread.
> 
> R=ahaas@chromium.org, mstarzinger@chromium.org
> 
> Bug: v8:9477
> Change-Id: I3598329e37482ebd27a13acc752581c714226184
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1735319
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63097}

Bug: v8:9477
Change-Id: Iac696f1ff3cd5209231a8dd8d1500cf77c2777b8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1739370
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63138}