feat(aria/menu): Add possibility to create a shared menu component from aria/menu

### Feature Description

When building a menu using [aria/menu](https://angular.dev/guide/aria/menu#menu-with-trigger) you have to have the following structure:

1. an for cdkConnectedOverlay
2. a container element with ngMenu
3. another for ngMenuContent
4. only then the actual ngMenuItem elements

This results in 4 structural levels that need to be repeated every time you need a new menu.

I attempted to create a shared menu component (similar to Angular Material’s MatMenu) in order to reduce this complexity to 2 levels and enable an API like:

```

Open Menu

mark_email_read
Mark as read

snooze
Snooze

```

Internally, app-menu wraps Menu and MenuContent:

```
@Component({
selector: 'app-menu',
imports: [OverlayModule, Menu, MenuContent],
template: `

`
})
export class AppMenu {
appMenuTrigger = input.required();
formatMenu = viewChild>('formatMenu');
overlayPositions: ConnectedPosition[] = [{originX: 'start', originY: 'bottom', overlayX: 'start', overlayY: 'top', offsetY: 4}];
}
```

and menu items are wrapped like this:
```
@Component({
selector: 'app-menu-item',
template: '',
hostDirectives: [{ directive: MenuItem, inputs: ['value: value'] }]
})
export class AppMenuItem {}
```

**Problem**
With this approach, accessibility breaks (keyboard navigation no longer works correctly). This seems to happen because `Menu` cannot properly register `MenuItem` children when they are content projected.

**Proposed enhancement**
Expose a public API on `Menu` that allows the menu to "refresh" in order to register the items when they are content projected.

### Use Case

_No response_