This changes the behavior of suppressTracing to be less problematic (or, problematic in a different way).

Today, because in the browser we do not have async context isolation, there is only a single shared top scope. Because of this, if you have code like this:

const spanPromise = suppressTracing(async () => {
  await new Promise(resolve => setTimeout(resolve, 100));
  return startInactiveSpan({ name: 'span' });
});

const span = startInactiveSpan({ name: 'span2' });

The span2 will also be suppressed, because suppressTracing forks the scope and sets data on it to ensure spans are not recorded. This is problematic as that will result in completely unrelated spans, e.g. pageload/navigation spans, being suppressed while e.g. an ongoing fetch call that is suppressed happens.

This PR changes this to instead only suppress tracing synchronously in the browser. This obviously is also not really ideal and can lead to things not being suppressed, but it feels like the better tradeoff for now.