Directional focus edge traversal behavior. (flutter#161285)

Fixes: flutter#160843 

This PR adds edge behavior feature for traversing focus using arrow
keys. This allows cycling through the focus within the `FocusScope` in a
closed loop using the arrow keys. Which may be needed by TV application
developers.

Additionally, as in case flutter#160843, `TraversalEdgeBehavior.parentScope`
can be used to allow nested Navigators to traverse focus beyond the
Navigator using arrow keys.

```dart
MaterialApp(
  home: Column(
    children: <Widget>[
      makeFocus(0),
      Navigator(
        onGenerateRoute: (RouteSettings settings) {
          return MaterialPageRoute<void>(
            traversalDirectionedEdgeBehavior: TraversalEdgeBehavior.parentScope,
            builder: (BuildContext context) {
              return Column(
                children: <Widget>[
                  makeFocus(1),
                  makeFocus(2),
                ],
              );
            },
          );
        },
      ),
      makeFocus(3),
    ],
  ),
);
```


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there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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Author: yiiim

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

@@ -42,6 +42,8 @@ class MaterialPageRoute<T> extends PageRoute<T> with MaterialRouteTransitionMixi
     super.fullscreenDialog,
     super.allowSnapshotting = true,
     super.barrierDismissible = false,
+    super.traversalEdgeBehavior,
+    super.directionalTraversalEdgeBehavior,
   }) {
     assert(opaque);
   }

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

@@ -1358,6 +1358,7 @@ class FocusScopeNode extends FocusNode {
     super.skipTraversal,
     super.canRequestFocus,
     this.traversalEdgeBehavior = TraversalEdgeBehavior.closedLoop,
+    this.directionalTraversalEdgeBehavior = TraversalEdgeBehavior.stop,
   }) : super(descendantsAreFocusable: true);
 
   @override
@@ -1374,6 +1375,13 @@ class FocusScopeNode extends FocusNode {
   /// and apply the new behavior.
   TraversalEdgeBehavior traversalEdgeBehavior;
 
+  /// Controls the directional transfer of focus when the focus is on the first or last item.
+  ///
+  /// Changing this field value has no immediate effect on the UI. Instead, next time
+  /// focus traversal takes place [FocusTraversalPolicy] will read this value
+  /// and apply the new behavior.
+  TraversalEdgeBehavior directionalTraversalEdgeBehavior;
+
   /// Returns true if this scope is the focused child of its parent scope.
   bool get isFirstFocus => enclosingScope!.focusedChild == this;