Upgrade the Dart/Flutter SDK to v4

[marandaneto]

To address:

1. Should we create the Dart platform and make this a fallback to Flutter? like Java/Android
2. Should we make Dart v3 a legacy like Java does and new docs are only v4? (Like Java v1 and v3)
3. Do we need a migration page or just the new docs like Java docs? so with all the samples, people can learn the difference anyway.

cc @bruno-garcia @rxlabz
open for early feedback, obviously there's nothing yet, but the questions above would be nice to discuss @bruno-garcia

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[marandaneto]

Flutter platform only for now.
PR for flutter cookbook once v4 is GA.
Migration page.

[marandaneto]

TODO (if they make sense):

decluttering
drain-example
getting-started-next-steps
getting-started-primer

[bruno-garcia]

Beautiful :)

It's odd that we say Health here because there's no support for release health. But the docs talk about release which makes sense.

IHMO showing this is just noise and should be deleted:

Can we opt out from this?

[bruno-garcia]

1 last fix: Hide the User Feedback page:

https://sentry-docs-git-ref-flutter-v4.sentry.dev/platforms/flutter/enriching-events/user-feedback/

Other than that looks good to merge already! We can do another iteration after that for any details

[marandaneto]

1 last fix: Hide the User Feedback page:

https://sentry-docs-git-ref-flutter-v4.sentry.dev/platforms/flutter/enriching-events/user-feedback/

Other than that looks good to merge already! We can do another iteration after that for any details

good catch, I've hidden for dart but looks like we need both