test(nextjs): Run nextjs-16 on Bun, Deno and Cloudflare - #24999

nextjs-16 gets variants for Bun, Deno and Cloudflare Workers (OpenNext) and
replaces `nextjs-16-bun` and `nextjs-16-cf-workers`. Bun, Cloudflare and
Cloudflare with the latest Next.js are required jobs, as the two old apps
were. Deno is optional.

- Bun and Deno run `next start` on the same build as Node.js. The server
  config adds the integrations of `@sentry/bun` and `@sentry/deno` that
  replace the Node.js instrumentation these runtimes do not trigger. The
  e2e README now describes this, and that `variants` run as required jobs.
- Cloudflare builds with `opennextjs-cloudflare` and wraps the Worker in
  `worker.ts` with `withSentry` from `@sentry/nextjs/cloudflare`.
  `pg-cloudflare` is in `serverExternalPackages`, because OpenNext copies the
  `workerd` build of a package only when that list has the package.
- The app does not depend on `@opentelemetry/api` directly, because the
  OpenNext middleware bundle can not load an installed copy.
  `/api/otel-context` uses the copy of Next.js.
- The mock AI server runs in the Playwright global setup instead of the app,
  because a Worker can not start a `node:http` server. Thus the OpenAI test
  runs on every runtime.
- Tests branch on `getRuntime()` where the runtimes differ (segment origin
  and attributes, middleware spans in the request segment of the Worker,
  fetch span attributes). They skip what a runtime can not do: Node.js
  runtime metrics on Workers, and `pg` spans on Bun and Workers, which have
  no runtime module hook.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>