[v9]: Change `SENTRY_NATIVE_BACKEND` behavior if not set

[buenaflor]

Description

Probably we would use crashpad as default

see #2522

[buenaflor]

@vaind do you know what's the state for this? as far as I know we've had issues with crashpad on vs

[vaind]

Good point for bringing this up. I believe we should definitely reenable the native backend by default in v9 bump. Yes, it broke some people using old out-of-support Visual Studio versions which was a no-go for a minor version but it's not an issue for v9 to require them to update their toolchain.

Note, for arm64 we may need to use breakpad instead of crashpad: #2479 - we should check the current support status of sentry-native

[buenaflor]

for arm64 we may need to use breakpad instead of crashpad

Specifically only on windows or are there problems with linux arm64 and crashpad as well?

[vaind]

just windows AFAIR