Add fireShortcut method to ComponentTester for component-level keyboard shortcuts

[Copilot]

This PR adds a fireShortcut() method to the ComponentTester class to enable testing of keyboard shortcuts attached directly to components through the KeyNotifier interface methods.

Problem

The existing fireShortcut() method in BaseUIUnitTest only works with shortcuts attached to the UI (or modal components) created with the Shortcuts API. It does not work with key down listeners attached to individual components through the KeyNotifier interface methods like addKeyDownListener().

Solution

Added a new fireShortcut(Key key, KeyModifier... modifiers) method to ComponentTester that:

• Uses ShortcutsKt._fireShortcut() with the wrapped component as specified in the issue
• Validates component usability before firing the shortcut using ensureComponentIsUsable()
• Follows the same method signature and pattern as the existing UI-level fireShortcut() method
• Includes comprehensive JavaDoc explaining when to use this vs the UI-level method

Usage Example

@Test
void testComponentKeyboardShortcut() {
    MyComponent component = new MyComponent();
    component.addKeyDownListener(event -> {
        if (event.getKey() == Key.KEY_S && event.getModifiers().contains(Key.CONTROL)) {
            // Handle Ctrl+S shortcut
        }
    });
    
    getCurrentView().add(component);
    ComponentTester<MyComponent> tester = test(component);
    
    // Fire shortcut directly on the component
    tester.fireShortcut(Key.KEY_S, KeyModifier.CONTROL);
    
    // Verify the shortcut was handled...
}

Implementation Details

• Minimal changes: Only added necessary imports and the single method to ComponentTester
• Consistent API: Same method signature as BaseUIUnitTest.fireShortcut()
• Proper validation: Ensures component is usable (enabled, attached, visible, not behind modal)
• Clear documentation: Explains the difference between component-level and UI-level shortcuts

Tests Added

• Unit tests for method behavior and validation
• Integration tests demonstrating DOM listener interaction
• Example tests showing practical usage patterns

Fixes #1748.

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

• maven.vaadin.com
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.10/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.10/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.10 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.10/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/testbench/testbench org.codehaus.plexus.classworlds.launcher.Launcher clean compile -q (dns block)
  • Triggering command: /usr/lib/jvm/temurin-17-jdk-amd64/bin/java --enable-native-access=ALL-UNNAMED -classpath /usr/share/apache-maven-3.9.10/boot/plexus-classworlds-2.9.0.jar -Dclassworlds.conf=/usr/share/apache-maven-3.9.10/bin/m2.conf -Dmaven.home=/usr/share/apache-maven-3.9.10 -Dlibrary.jansi.path=/usr/share/apache-maven-3.9.10/lib/jansi-native -Dmaven.multiModuleProjectDirectory=/home/REDACTED/work/testbench/testbench org.codehaus.plexus.classworlds.launcher.Launcher clean compile -q -pl vaadin-testbench-unit-shared (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to my firewall allow list

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