New API:getActiveBaggage?

[cartermp]

This is inspired by two things:

• Code in the demo app that gets the current baggage and snags data from it
• The .NET baggage API which defines a Current property to get/set whatever the current baggage is from the active context

This api could work similar to getActiveSpan, wherein the getActiveBaggage API just calls propagation.getBaggage(api.context.active()).

Working with baggage is much less common than getting the current/active span, though, so the relative importance is low. I just think that every time you have to write api.context.active() and you're not doing super fancy context stuff, that smells like a need for an API 🙂

[dyladan]

I would support this addition