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}