Restart onError sampling for replays after stopping

### Problem Statement

We received the following message from a customer:

One account in our team has multiple roles that can be switched. We hope that when the user switches roles, the errors that occur will be recorded in a new Replays.
The latest version does not have replay.setupOnce(). Simply using replay.stop() and replay.start() will not generate new Replays. I only want to use replaysOnErrorSampleRate, because if replaysSessionSampleRate or tracesSampleRate is used, replay.start() will be executed when switching users, and then a Replay without error records will be generated.

### Solution Brainstorm

Expose a public API to allow for restarting of onError sampling after replay has been stopped.

### Product Area

Replays

Start by reviewing the replay lifecycle around replay.stop() and replay.start(), focusing on how replaysOnErrorSampleRate behaves after stopping. Define the public restart behavior so switching roles can create a new error-triggered Replay without enabling session or trace sampling. The issue names no files or tests, so those entry points must be located first.

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