test(e2e): Verify RN↔WebView connected trace in sample app

[antonis]

Outcome

The sample RN app gains a WebView screen that loads a page running @sentry/browser, and an automated check asserts the connected trace.

Acceptance criteria

• Sample screen renders a WebView with the integration enabled against an allow-listed test page that runs @sentry/browser.
• E2E asserts the WebView-originated event and the RN event share one trace_id.
• Runs on iOS + Android, New + Old Architecture.

References

• Meta-tag continuation contract: https://docs.sentry.io/platforms/javascript/tracing/distributed-tracing/

[linear-code]

RN-798