[v8] Remaining things to deprecate before v8 #10033
Description
These things still need to be deprecated (and/or a replacement written) before v8:
### Tasks
- [ ] `getCurrentHub()` - @deprecated & migration docs
- [ ] `startTransaction()` - @deprecated & migration docs
- [ ] All methods and properties on `Hub` interface
- [ ] https://github.com/getsentry/sentry-javascript/issues/10184
- [ ] All methods and properties `Transaction` that do not exist on OTEL spans
- [ ] lastEventId - make global method/variable
- [ ] `scope.setClient()` & update `Sentry.getClient()` to use scope clients (if set)
- [ ] `client.init()` instead of `client.setupIntegrations()` as public API
- [ ] makeMain()