Notify Flutter inspector when navigating widget tree with keyboard

[muhammadkamel]

Fixes #9809

This PR updates keyboard navigation in the Inspector widget tree so that moving selection with the up/down arrow keys notifies the Flutter inspector, matching the behavior of selecting a widget with the mouse.

Previously, keyboard navigation updated the selected row in DevTools but did not notify the connected Flutter app. Now setSelectedNode is called with notifyFlutterInspector: true during keyboard navigation, so the selected widget is reflected in the running app as expected.

Added tests for both direct controller navigation and keyboard event navigation.

Tested with:

/Users/mohammadkamel/otlob.tech/flutter_fork/bin/flutter test test/screens/inspector/inspector_tree_test.dart

Result: 8 passed.

No before/after screenshots are included because this change does not alter the visual UI; it fixes keyboard interaction behavior.

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[gemini-code-assist]

Code Review

This pull request updates the InspectorTreeController to notify the Flutter inspector during keyboard navigation and adds corresponding widget tests. Feedback suggests optimizing the tree refresh logic by returning the result of the selection update to avoid unnecessary refreshes and refactoring duplicate helper functions in the test file to adhere to DRY principles.