fix(radio): dispatch input event on keyboard navigation

[ErnestHysa]

Fixes #5949

Dispatches an InputEvent before the change event when keyboard-navigating radio buttons with arrow keys, matching native <input type='radio'> behavior where both input and change events fire on user interaction.

Changes

• Modified SingleSelectionController.handleKeyDown in radio/internal/single-selection-controller.ts to dispatch an InputEvent before the change event
• Added test in radio/radio_test.ts to verify input event is dispatched on keyboard navigation

Testing

Added a new test case dispatched an input event on user navigation that verifies the input event is fired when using arrow keys to navigate radio buttons.

[google-cla]

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[ErnestHysa]

CLA flag noted — checking the linked Google account. The change itself is a small dispatch tweak in single-selection-controller.ts with a test in radio_test.ts; happy to address any review feedback once the CLA clears.

[asyncliz]

@ErnestHysa it looks like the commit was made with the @ernest account, which hasn't signed the CLA. Can you either amend the commit using your other account with a forced update, or sign the CLA for that account?

[asyncliz]

Thanks for your patience! This LGTM