Maps set on the JSFunction were done so in a non-atomic way, which meant
that we were failing to have a synchronization point and the read/writes
could be reordered.

This started happening after a previous CL[1] moved some methods from
relaxed to non-atomic, which triggered TSAN (see v8:11696).

[1]: https://chromium-review.googlesource.com/c/v8/v8/+/2843359

Bug: v8:7790, v8:11696
Change-Id: I8472ff8b63d391376ee2f1dcf0a8b4fd7cecfcd1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2851893Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74357}