Session Replay across multiple iframes simultaneously

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

1. On a top level domain, open two iframes that both initialize Sentry Replay
2. Interact with both iframes

### Expected Result

Unsure what would be the best expected result, but the current behaviour seems random. Potential solutions:
1. Show two separate DOMs in the Replay UI
2. Allow setting programmatically which iframe is selected for DOM playback as the session is happening.

### Actual Result

It seems to randomly pick which iframe the replay session will use for its DOM. It will randomly switch between the two as the replay plays. You will, however, get breadcrumbs from both iframes within the one replay session. So both iframe sessions are being bundled together, but the replay UI is not able to show both and/or pick a single iframe to focus on.

### Product Area

Replays

### Link

https://coefficient.sentry.io/replays/88270d71a41c4facad571f909326d3f6/

### DSN

_No response_

### Version

_No response_

Reproduce the issue by opening two iframes that both initialize Sentry Replay and interacting with each. Start by reviewing the linked replay and the Replays product behavior around combined breadcrumbs and DOM playback. Done means the expected iframe playback behavior is decided and the replay no longer switches unpredictably between iframe DOMs.

Written by the indexing model from the issue text.