Auto detect `inApp` for stack frames

### Problem Statement

`inApp` for non Android has to be set via `inAppIncludes`. It would be nice if Sentry could auto detect `inApp` frames.

### Solution Brainstorm

- Check if a package can be found on sources like https://central.sonatype.com/?smo=true
- might be rate limited
- not sure we can check package directly or need to try and walk up the package tree and try each package
- open source app could be on there but still be inApp
- Check what's calling Sentry.init - probably just shifting guesswork as we then don't know how far up the package tree we still consider inApp (e.g. com.some.myapp.x.y.MySpringApp might be in app but com.some.mylib could be a library by someone else
- If we have sources for a frame, assume it's inApp=true (wouldn't work in case we reworked source context to something that's loaded lazily when an issue is displayed and we then also lookup sources from https://central.sonatype.com/?smo=true etc.)
- During compile time detect package in build tool plugin somehow (Gradle and Maven)
- For integrations with auto init we may be able to find out some config param or similar that tells us something about the package