Tidyup animations sample (#1672)

* Tidyup

* Drop `flutterAnimateDemos`

animations/lib/src/basics/animated_container.dart

@@ -12,7 +12,7 @@ Color generateColor() => Color(0xFFFFFFFF & Random().nextInt(0xFFFFFFFF));
 
 class AnimatedContainerDemo extends StatefulWidget {
   const AnimatedContainerDemo({super.key});
-  static String routeName = 'basics/01_animated_container';
+  static String routeName = 'basics/animated_container';
 
   @override
   State<AnimatedContainerDemo> createState() => _AnimatedContainerDemoState();

animations/lib/src/basics/basics.dart

@@ -0,0 +1,8 @@
+export 'animated_builder.dart';
+export 'animated_container.dart';
+export 'animation_controller.dart';
+export 'custom_tween.dart';
+export 'fade_transition.dart';
+export 'page_route_builder.dart';
+export 'tween_sequence.dart';
+export 'tweens.dart';