Previously both tracing implementations would be run side-by-side when
perfetto was enabled with the V8_USE_PERFETTO build flag. This CL
makes them run separately.

Both implementations now use the trace file provided by the user in D8
or the default v8_trace.json.

Add tests for perfetto events (which must be tested differently
due to the proto output format).

Drive-by fix: Fix pass-by non-const ref in GetJSONStrings.

Remove the TraceEvent struct for testing; we can just store a copy of
the protobuf directly.

Bug: v8:8339
Change-Id: Id50003e0f96e44b99a63a26693da6bdaca989504
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1702619Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62810}