[sdk-trace] make activeSpanProcessor private

[pichlermarc]

Description

activeSpanProcessor is currently public and that allows users to modify the span processor by setting it on the fly even though the should be done via addSpanProcesssor() or - ideally - only via the constructor as the user is not supposed to hold on to the SDK instance of the TracerProvider after the initialization phase, as this can have unintended side-effects on the exported telemetry and should therefore be avoided.

This issue is considered done when

• the activeSpanProcessor property at

  opentelemetry-js/packages/opentelemetry-sdk-trace-base/src/BasicTracerProvider.ts

  Line 73 in 47444f2

  activeSpanProcessor: SpanProcessor;

  has been marked private or protected
• it has been verified that activeSpanProcessor is not public in any other way for the BasicTracerProvider
• it has been verified that activeSpanProcessor is not public in any other way for the WebTracerProvider
• it has been verified that activeSpanProcessor is not public in any other way for the NodeTracerProvider

[legalimpurity]

@pichlermarc can I pick this up?