fix(radio): dispatch input event on keyboard navigation

[akinshaywai]

Problem

Fixes #5447

Native <input type="radio"> fires both input and change events when a radio button is selected via arrow key navigation. <md-radio> only dispatches change, which means:

• React users miss keyboard selections because React's onChange maps to the DOM input event, not change
• Any listener specifically watching for input events is silently skipped on keyboard navigation

Fix

In SingleSelectionController.handleKeyDown, fire an InputEvent('input', { bubbles: true, composed: true }) before the existing change event, matching native <input type="radio"> order and behavior:

• composed: true so the event crosses shadow DOM boundaries (same as native)
• input fires before change (same order as native)

A new test dispatches an input event on user navigation is added alongside the existing dispatched a change event on user navigation test.

Testing

// Before fix – input handler never called on ArrowRight
radio.addEventListener('input', () => console.log('input fired'));

// After fix – fires on both click and arrow key navigation

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