Reland "[VM/Timeline] Add Dart_RecordTimelineEvent Embedder API to support reporting flow events that can be serialized in Perfetto's format"

Patchset 1 is a reland of commit
f52bdb96aa4a0d7c965ab79ade9615777107cd46, and Patchset 2 adds a
corrected reland of commit 0d0e301979a19ad71df59645562a501db19a0baf.

The leak in g3 was caused by moving the `state_ = 0;` line before the
`owns_label()` check in `TimelineEvent::Reset`.

TEST=Ran the g3 tests that were failing on a cbuild copy with these
changes (sponge2/1134a5bb-5168-4e4c-bb03-72a7d7ad6ab4).

Original change's description:
> [VM/Timeline] Add Dart_RecordTimelineEvent Embedder API to support reporting flow events that can be serialized in Perfetto's format
>
> Added a deprecation notice to Dart_TimelineEvent as well.
>
> TEST=Used the embedder API to report an events of each of the following types:
> Dart_Timeline_Event_Begin, Dart_Timeline_Event_Duration,
> Dart_Timeline_Event_Instant, Dart_Timeline_Event_Async_Begin, and
> Dart_Timeline_Event_Async_Instant, each associated with flow IDs. Then,
> retrieved the trace using GetPerfettoVMTimeline and checked that flow arrows
> were displayed correctly in the Perfetto trace viewer.
>
> Change-Id: I82e49554b5970767e306dc4149a782e99a5c6512
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/302963
> Commit-Queue: Derek Xu <derekx@google.com>
> Reviewed-by: Ben Konyi <bkonyi@google.com>

Change-Id: I08783d6b5575fb3fe43da3203e58902bf9b7d038
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/308721
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Derek Xu <derekx@google.com>