refactoring to avoid too many imports

[kellvembarbosa]

@super-bryan Hello, I hope you are well,

Yesterday I integrated the Superwall package into my application, today after updating the package I had problems with the import paths.

Instead of just reporting the problem, I decided to contribute.

It is a good practice in Flutter to work with a main file that informs all public files, this file is in the lib folder in the root;

Examples in other packages:

• https://github.com/jonataslaw/getx/blob/master/lib/get.dart
• https://github.com/flutter/packages/blob/main/packages/go_router/lib/go_router.dart

I also added all the sub-folders inside the 'lib/src' folder to avoid a suggestion to import these files by the VSCode, so it will suggest only the main file previously created.

Exemples in other packages:

• https://github.com/flutter/packages/tree/main/packages/go_router/lib
• https://github.com/rrousselGit/provider/tree/master/packages/provider/lib

This way it avoids easily breaking projects that depend on the superwallkit_flutter package.

Thank you for supporting Flutter 💙

[super-bryan]

Hey @kellvembarbosa thanks a ton for this! I'll make sure this makes its way in to the release 🙂

Just a heads up – we're not quite ready to onboard customers to Flutter just yet, so I'd hold off on your implementation until we send out a launch email. Hopefully later this week!

[super-bryan]

@kellvembarbosa there was a bit of drift between this PR and some of the refactoring work we've been doing. I went ahead and made the changes you made in this PR in this commit (f356306ee90553d56db64595847b95a99453813b). Thanks again!