trace_events: add traced_value.cc/traced_value.h

Port of the V8 internal v8::tracing::TracedValue that allows
structured data to be included in the trace event. The v8 class
is not exported in the public API so we cannot use it directly.

This is a simplified and slightly modified port. This commit only
adds the class, it does not add uses of it. Those will come in
separate PRs/commits.

PR-URL: https://github.com/nodejs/node/pull/21475


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>