Creates a span. This span is not set as active, so will not get automatic instrumentation spans as children or be able to be accessed via Sentry.getSpan().

If you want to create a span that is set as active, use startSpan.

Note that if you have not enabled tracing extensions via addTracingExtensions or you didn't set tracesSampleRate or tracesSampler, this function will not generate spans and the span returned from the callback will be undefined.