This is a reland of be52501d

Fix data race by not emitting the epoch for sweeper background jobs
at them moment.

Original change's description:
> [heap] Add epoch to GC tracing events
>
> This CL adds the TRACE_GC_EPOCH macro, which adds the epoch as attribute
> to the trace event. Use TRACE_GC_EPOCH for top-level events, nested
> events can get the information from its parent.
>
> V8's GC needs an epoch for young and full collections, since scavenges
> also occur during incremental marking. The epoch is also process-wide,
> so different isolates do not reuse the same id.
>
> Change-Id: I8889bccce51e008374b4796445a50062bd87a45d
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2565247
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#71521}

Change-Id: Ib8f4bfdc01c459955eb6db63bb6e24a8aa068f09
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2567702
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71567}