Remove references to @required in favor of the keyword (#79239)

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

@@ -874,7 +874,7 @@ abstract class FloatingActionButtonAnimator {
   ///
   /// ```dart
   ///   @override
-  ///   Animation<double> getScaleAnimation({@required Animation<double> parent}) {
+  ///   Animation<double> getScaleAnimation({required Animation<double> parent}) {
   ///     // The animations will cross at value 0, and the train will return to 1.0.
   ///     return TrainHoppingAnimation(
   ///       Tween<double>(begin: 1.0, end: -1.0).animate(parent),
@@ -896,7 +896,7 @@ abstract class FloatingActionButtonAnimator {
   ///
   /// ```dart
   /// @override
-  /// Animation<double> getRotationAnimation({@required Animation<double> parent}) {
+  /// Animation<double> getRotationAnimation({required Animation<double> parent}) {
   ///   return Tween<double>(begin: 0.0, end: 1.0).animate(parent);
   /// }
   /// ```

packages/flutter/lib/src/widgets/framework.dart

@@ -479,10 +479,9 @@ abstract class Widget extends DiagnosticableTree {
 /// ```
 /// {@end-tool}
 ///
-/// By convention, widget constructors only use named arguments. Named arguments
-/// can be marked as required using [@required]. Also by convention, the first
-/// argument is [key], and the last argument is `child`, `children`, or the
-/// equivalent.
+/// By convention, widget constructors only use named arguments. Also by
+/// convention, the first argument is [key], and the last argument is `child`,
+/// `children`, or the equivalent.
 ///
 /// See also:
 ///
@@ -716,10 +715,9 @@ abstract class StatelessWidget extends Widget {
 /// ```
 /// {@end-tool}
 ///
-/// By convention, widget constructors only use named arguments. Named arguments
-/// can be marked as required using [@required]. Also by convention, the first
-/// argument is [key], and the last argument is `child`, `children`, or the
-/// equivalent.
+/// By convention, widget constructors only use named arguments. Also by
+/// convention, the first argument is [key], and the last argument is `child`,
+/// `children`, or the equivalent.
 ///
 /// See also:
 ///