refactor(device_info_plus)!: Change nullability for AndroidDeviceInfo properties

[vbuberen]

Description

It seems that during migration to null safety all properties for Android platform were just marked as nullable, while in reality almost all properties are not nullable. Thus, we had issues like #706 with users not really understanding why something is nullable now.

I refactored the plugin interface to have only a few properties which really can be null declared as nullable, while the rest if non-nullable anymore.

Related Issues

#706

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.