OT Bridge: Decide whether to activate DistContext/TagMap or not

[carlosalberto]

OpenTracing's SpanContext contains Baggage, which is backed up internally by an instance of DistributedContext (previously called TagMap), which works seamlessly underneath.

One thing to decide is whether we want to also set this aforementioned DistributedContext object as active when its 'parent' Span is set as the active instance:

try (Scope scope = io.opentracing.Tracer.activate(Span)) {
  // The wrapped io.opentelemetry.trace.Span *is* set active
  // The wrapped io.opentelemetry.distributedcontext.DistributedContext **is not**
}

There are a few possible challenges here, such as doing the deactivate/activate step of DistributedContext when the Baggage changes from the OT Bridge side, while keeping other components in the proper activation stack order (either other Span/DistributedContext objects).

[carlosalberto]

Closed on behalf of #3049 as the discussed changes are already covered by the aforementioned issue.