fix: Improved getting active tracer and current span mechanism

[CagriYonca]

get_tracer_tuple function is widely used in almost every instrumentation and basically it returns the active_tracer and the parent_span if a root exit span is not expected, otherwise it returns only the active span. If neither the current_span is recording nor a root exit span is expected, it returns None. Before the code change, get_current_span function was called twice, the active_tracer was reached via singletons.tracer instead of the tracer getter (get_tracer).

tracing_is_off function is also widely used in almost every instrumentation and it only returns whether the tracer is ready to record a new span or not. As I already explained above, we already have this information in the tracer, so that by combining these two functions into get_tracer_tuple function, we're getting rid of 1 get_current_span call and functionality of tracing_is_off function since we can directly check if the tracer in the instrumentation is False or not.

• get_active_tracer and tracing_is_off functions has been removed
• adapted instrumentations to the new get_tracer_tuple function
• observed that rpc-client spans started being created when the root exit span is enabled for the following instrumentations:
  • google cloud pubsub
  • grpcio