Investigate and align current session replay behaviour

[philprime]

Description

When starting the Cocoa SDK with session replay only running in buffer mode (sessionSampleRate set to 0, with onErrorSampleRate set to > 0) the SDK will record frames and only create a session replay video when capturing an error or exception event. The first replay event is the using the replay_type = buffer and then switches to replay_type = session in further video segments.

The documentation added in getsentry/sentry-docs#14462 mentions that the replay type must not change.

Investigate the current setup and adapt according to the documentation.

[linear]

COCOA-499 Investigate and align current session replay behaviour

[philprime]

One aspect of this is that the reported sample rates don't correlate with the replay type, e.g. the session sample rate is 0 but the type is session.

See #4866 for an example use case.