Consider using the Global scope for static APIs (like setUser...)

### Description

On react native context, where we only have one user, Sentry.SetUser could use the global scope instead of an isolation scope.<br>We could target v7 with this change.

context: [https://github.com/getsentry/sentry-react-native/pull/4901#discussion_r2142456956](<https://github.com/getsentry/sentry-react-native/pull/4901#discussion_r2142456956>)