Support native crash reporting for Windows

Sentry SDK for Flutter supports Windows since it's preview versions: https://github.com/getsentry/sentry-dart/pull/407
Since then, Flutter has made Windows support GA: https://medium.com/flutter/announcing-flutter-for-windows-6979d0d01fed

But it does not capture a native crash. The goal is to use [sentry-native](https://github.com/getsentry/sentry-native) with the crashpad backend to capture minidumps on Windows.

This was recently done on the Unity SDK:

* https://github.com/getsentry/sentry-unity/issues/527

This tracking issue contains the items we would consider when adding support to Flutter. Including:

- [ ] Offline caching on by default
- [ ] Crash free rate to rely on the native layer (ask native: did I crash last run?)
- [ ] Scope sync so data set to the SDK in Dart, shows up in native crashes
- [x] Make sure we can bundle `crashpad_handler.exe` with the final app
- [x] Upload symbols automatically during build. (might require changes to: https://github.com/getsentry/sentry-dart-plugin)

Related:
* https://github.com/getsentry/sentry-dart/issues/433
* https://github.com/getsentry/sentry-dart/issues/487
* https://github.com/flutter/flutter/issues/108974
* https://github.com/getsentry/sentry-native/issues/818