RadioButtonGroup fires focus events when moving between options

Moving keyboard focus between options inside a Desktop RadioButtonGroup incorrectly fires FocusLost and FocusReceived for the whole group. This can trigger validation or message boxes even though the user is still interacting with the same control.

The group should behave as one focus area: FocusReceived should fire when focus enters the group, and FocusLost should fire when focus leaves it. Choosing another option should continue to raise SelectionChanged normally.