refactor(samples): Convert main screen to Jetpack Compose

[markushi]

📜 Description

Converts the MainActivity from Java to Kotlin, categorizing all our buttons a bit nicer too.

requires #5016 to be merged first.

💡 Motivation and Context

Modernizes the sample app to use Kotlin, which is now the recommended language for Android development. This makes the sample more representative of current best practices and simplifies future enhancements.

💚 How did you test it?

Manual testing of the sample app to ensure functionality remains unchanged.

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

#skip-changelog