material_ui package migration

[jt274]

Migrate to the new material_ui package which has been decoupled from the flutter framework in flutter 3.47.0: https://flutter.dev/blog/whats-new-in-flutter-3-47

Require dart >=3.5.0 and flutter >=3.47.0

All flutter analyze warnings are cleared, all lint issues fixed and I fixed one bug in country_selector_base.dart where a variable was being assigned to itself.

Checklist

• I have bumped the version in pubspec.yaml
• I have added an entry in changelog.md for the new pubspec version
• (if applicable) I have added "Closes #1234" to this termplate to automatically close related issues.
• (not required if no sensible change has been made eg: Localization) I have added tests that prove my fix is effective or that my feature works.

[cedvdb]

Thanks @jt274 let's see if this one deploys correctly

[jt274]

@cedvdb It looks like it may have failed because the version tag already exists. Do you want me to submit a new PR with the version 2.0.1, or will you take care of it?

[cedvdb]

@jt274 yes I don't have access to my laptop this weekend so if you can resubmit as 2.0.1 this could fix the release.

[jt274]

@cedvdb submitted here: #47