`vscode-radio-group`: Arrow key selection changes checked radio but does not dispatch change

[msengkhyavong]

Steps:

1. Render a vscode-radio-group with two vscode-radio options.
2. Attach change / React onChange to the group.
3. Tab into the group, use ArrowDown/ArrowUp/ArrowLeft/ArrowRight to move between options.

Actual:

• Visual checked state and focus move to the new option
• No change event fires (handler not called)

Expected:

• When arrow keys change selection, the component should dispatch change (or provide a documented event) so consumers can update state.
• This aligns with APG radio group behavior where arrow keys change which radio is checked