Native crashes should include similar context available in C# events

[bruno-garcia]

Native crashes currently only include the data set via scope sync and what came from the minidump.
A lot of the context data in C# events are added via the UnityEventProcessor, which doesn't run for native.

On Android, (sentry-native support isn't done with crashpad) the native layer writes an envelope to disk which the Java layer picks up and adds context to. There are trade offs there, some disadvantages are the serialization round trip, protocol mismatch between layers (the .NET SDK doesn't keep values it doesn't have typed in C#) and the need of the process being relaunched, so the managed layer can do its job.

One alternative is to provide the 'static' (device info, unity version, etc) data via init to sentry-native. The question remains about data that changes, that's not available on Android events either.

[bruno-garcia]

Dupe of #650