Allow to access installationId

[M123-dev]

From the docs https://docs.sentry.io/platforms/dart/enriching-events/identify-user/

If you don't provide an id, the SDK falls back to installationId, which the SDK randomly generates once during an app's installation

It would be great if there'd be a way to access thid id. If I understood it correctly, it is possible to set a own SentryUser with a custom uuid instead, but this would destroy all previous user records.

[marandaneto]

If you set an user without the "id", the installationId is merged with your user before the event is sent, its a quick workaround for now.

[M123-dev]

That would be good, sadly this doesn't seem to work for me

    String? sentryId = 'error';
    await Sentry.configureScope((Scope s) => s.setUser(SentryUser()));
    await Sentry.captureMessage('Test message');
    await Sentry.configureScope((Scope s) => sentryId = s.user?.id.toString());
    print(sentryId);

I/flutter (12272): null

[kuhnroyal]

Try to inspect it in the beforeSend callback, thats when it should be there.

[marandaneto]

Relates to getsentry/team-mobile#11 as well since the data is not in the beforeSend for Android.

[marandaneto]

Closing in favor of #1556 which will address this.