fix: expand/collapse interaction in navmenu

[mrpmorris]

1. Clicking the main expand/collapse button for the whole menu stutters when custom icon content is used.
2. It should toggle when enter is pressed.
3. It should expand when ArrowRight is pressed.
4. It should collapse when ArrowLeft is pressed.

The same rules should apply for FluentNavMenuGroup, with the additional

1. When a group expands, it should notify the FluentNavMenu so it can automatically expand if required.