Bump required min SDK and add CI check

[kuhnroyal]

• required due to meta: ^1.7.0 dependency
• required due to invalid plugin registrations prior to Flutter 2.8.0

[mateusfccp]

@kuhnroyal
It seems meta: 1.7.0 requires Dart 2.12, which is available since Flutter 2.0.
https://github.com/dart-lang/sdk/blob/5b39eb2f0183fde63ae7d7851e8bfaf6a4075998/pkg/meta/pubspec.yaml

Thus, I'm failing to understanding the objective of this PR. Could you clarify?

[kuhnroyal]

Flutter versions prior 2.8.0 use an older meta version (1.3.0 I think). Since this package forces 1.7.0, you have to use min Flutter 2.8.0.
And also the way the plugins are registered was reworked in Flutter 2.8.0 and that way is already used.
You simply can not use this package with Flutter versions <2.8.0.

[mateusfccp]

Yeah, I didn't want to break this package for <3, but it seems it's already broken for <2.8. I will accept your PR and release a last 2 versions (2.2) with these changes. Then, release a new breaking for Flutter 3.