Move Flutter widgets to packages directory

packages/flutter_widgets/lib/src/extension.dart

@@ -0,0 +1,14 @@
+extension StringExtension on String {
+  String capitalize() {
+    return "${this[0].toUpperCase()}${this.substring(1)}";
+  }
+}
+
+/// List extension
+extension IterableX<T> on Iterable<T> {
+  /// Insert any item<T> inBetween the list items
+  List<T> insertBetween(T item) => expand((e) sync* {
+        yield item;
+        yield e;
+      }).skip(1).toList(growable: false);
+}