chore: Modernize project setup

Update dependencies, move to Gradle KTs and overall improve build and project files.

android/app/src/debug/AndroidManifest.xml

@@ -1,3 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
     <uses-permission android:name="android.permission.INTERNET"/>
 </manifest>