docs: add section on modeling state

[EchoEllet]

Status

IN DEVELOPMENT/HOLD

Breaking Changes

No

Description

Add a new section Modeling States to covert the common approaches that are suggested by the Bloc library.

• We could extract the code examples as components
  so this section can be localizable without duplicating them.
• I haven't used Bloc in a fully scalable Flutter/Dart application yet, so I expect some minor or major design issues.
• The docs can be improved further.
  For example, we might consider providing different or better examples, as well as a minimal example of updating the state from the Bloc/Cubit though it can be out of scope for this section.
• The name status for the third approach could be improved or changed if needed.

We could consider closing this PR in case it's not suitable.

I'm open to all feedback, feel free to request any changes or commit them directly.

Screenshots

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[felangel]

LGTM thanks so much for the contribution! 💙

[EchoEllet]

Thank you for the feedback.