diagnostics_channel: add tracing channel

This adds a helper to present tracing functionality through a group of channels and a shared context object. The shared context object can be used to communicate meta information about the action being traced.

No effort is made to link traces together, this only provides the basics to express a span for a single sync or async task. It's left up to the user to track and link span data through something like AsyncLocalStorage.

Similar to #44894, I'm starting this as a draft and skipping docs for the moment to get feedback on the API design. If we settle on this design satisfying our needs I'll write up some proper docs for it.

cc @nodejs/diagnostics