Fixes #209 - retrieval of keyWindow/rootViewController.

[AndLen23]

This change will retrieve the rootViewController from the currently active scene to support the UISceneDelegate setup in Flutter/iOS.

The code is backward compatible with earlier versions than 13.0 of iOS.

[yashdeepsingh-create]

Any update on this?

[joachim-quis]

Important Notice: Repository Reset for v2.0

This repository is being reset for a complete v2.0 rewrite of flutter_contacts. The existing v1 codebase and full git history will be preserved in the legacy_v1 branch.

What this means for your PR:

• This PR will become unmergeable after the reset
• If your change is a feature or fix that's still relevant for v2, please review the new codebase after the migration and consider re-implementing it against the new main branch

Note that v2 is a complete rewrite with many new features including full macOS support, comprehensive vCard import/export, SIM contacts, contact groups, account management, blocked numbers, ringtone assignment, and more. This PR may already be addressed in v2.

Thank you for your contribution, and apologies for the inconvenience!