Report as app context what's the current activity during the error

[marandaneto]

I'd like to know which Activity/Screen was visible during the error (right now we only know if it's in the background or foreground). Right now it's only possible by looking at crumbs, I want to make this more visible. This should be searchable/alertable, I want to know which screens are getting more errors and alert only the screens I care the most. For transactions this is not needed since the Screen name is already the transaction name. I want to filter/alert errors that happened during screen X only.

For example, an error that happened after payment is less important than an error during the payment :P

### Tasks
- [ ] https://github.com/getsentry/sentry-java/issues/2664
- [ ] https://github.com/getsentry/sentry-cocoa/issues/3140
- [ ] https://github.com/getsentry/sentry-dart/issues/1411
- [ ] https://github.com/getsentry/sentry-react-native/issues/2994
- [ ] https://github.com/getsentry/relay/pull/2344

Other platforms to consider:

• [ ] .NET
• [ ] Unity

[romtsn]

We should define what would be the key for this in App context, this also requires some backend work to make it searchable, update relay with the new known key, etc.

[brustolin]

The navigation crumbs on Cocoa are based on viewDidAppear of UIViewControllers. While this helps you to understand which UIViewControllers are visible, it is not a reliable way of detecting on which screen the user currently is, as you can have nested UIViewControllers. On Android, we have a similar problem with single activity and fragments. So basically, we need a reliable way of reporting the current screen.

We could traverse the view controller tree to find out the root controller, but even this is not guaranteed to be correct.

[krystofwoldrich]

RN sends this information as a tag routing.route.name.

Could the key be:

event.contexts.app.screen event.contexts.app.view

[kahest]

As discussed for Cocoa here: https://github.com/getsentry/sentry-cocoa/issues/3140#issuecomment-1641992662

• we should consider adding a manual API to set the screen/activity for use cases where automatic detection doesn't work well (e.g. SwiftUI)

[marandaneto]

For android: https://github.com/skydoves/snitcher We can take a look at how on they track "current screen" for crashes.