We pretty much always want tracing data as a JSON file. Implement a
Consumer which converts protos to the JSON trace events format.

This duplicates a lot of the internals of TraceWriter in
trace-writer.cc but we will remove that eventually.

Cq-Include-Trybots: luci.v8.try:v8_linux64_perfetto_dbg_ng
Bug: v8:8339
Change-Id: I85f86562f1b3c4d24ecd755413d1c3f88b292adb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1541042
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61366}