feat(native): add option for new native crash backend

[JoshuaMoelans]

We released an experimental alternative crash backend in getsentry/sentry-native#1433 which aims to (long-term) replace the existing backends by our own Sentry-maintained one. We're experimentally exposing this in native, but this might be a solution to the issues we've been seeing here on Flutter w.r.t. Crashpad.

Related PR(s):

• Add native backend support for Windows and Linux sentry-unreal#1295

[linear-code]

DART-333

[buenaflor]

Should resolve #3103

[buenaflor]

I'll set this issue to blocked until we can confidently use it as it is still experimental