Fix classes that shouldn't be extended/instantiated/mixedin (#120409)

packages/flutter/lib/src/material/animated_icons/animated_icons_data.dart

@@ -25,6 +25,9 @@ part of material_animated_icons; // ignore: use_string_in_part_of_directives
 ///
 ///  * [Icons], for the list of available static Material Icons.
 abstract class AnimatedIcons {
+  // This class is not meant to be instantiated or extended; this constructor
+  // prevents instantiation and extension.
+  AnimatedIcons._();
 
   /// The Material Design add to event icon animation.
   ///

packages/flutter/lib/src/material/material_state.dart

@@ -632,7 +632,6 @@ class _MaterialStateUnderlineInputBorder extends MaterialStateUnderlineInputBord
 ///
 /// {@macro flutter.material.MaterialStateProperty.implementations}
 abstract class MaterialStateProperty<T> {
-
   /// Returns a value of type `T` that depends on [states].
   ///
   /// Widgets like [TextButton] and [ElevatedButton] apply this method to their

packages/flutter_driver/lib/src/extension/extension.dart

@@ -255,7 +255,6 @@ abstract class FinderExtension {
 /// See also:
 ///   * [CommandWithTarget], a base class for [Command]s with [Finder]s.
 abstract class CommandExtension {
-
   /// Identifies the type of command to be used by the driver extension.
   String get commandKind;