message: fix(nextjs): Export `BrowserTracing` integration directly
  This applies the changes made in (exporting `BrowserTracing` outside of `Integrations`, in order that it be treeshakable if necessary) to the nextjs SDK, which got left out of that PR.
  Fixes
diff: @@ -11,6 +11,22 @@ export { nextRouterInstrumentation } from './performance/client';
  export const Integrations = { ...BrowserIntegrations, BrowserTracing };
  +// This is already exported as part of `Integrations` above (and for the moment will remain so for
  +// backwards compatibility), but that interferes with treeshaking, so we also export it separately
  +// here.
  +//
  +// Previously we expected users to import `BrowserTracing` like this:
  +//
  +// import { Integrations } from '@sentry/nextjs';
  +// const instance = new Integrations.BrowserTracing();
  +//
  +// This makes the integrations unable to be treeshaken though. To address this, we now have
  +// this individual export. We now expect users to consume BrowserTracing like so:
  +//
  +// import { BrowserTracing } from '@sentry/nextjs';
  +// const instance = new BrowserTracing();
  +export { BrowserTracing };
  +
  /** Inits the Sentry NextJS SDK on the browser with the React SDK. */
  export function init(options: NextjsOptions): void {
  buildMetadata(options, ['nextjs', 'react']);
  