Use value task in INavigationProvider

[MikeAlhayek]

Currently, the navigation provider returns a Task.

public interface INavigationProvider
{
    Task BuildNavigationAsync(string name, NavigationBuilder builder);
}

In most implementations we do not need a task. I suggest changing that to return ValueTask instead. INavigationProvider is evaluated on every request and we could benefit from this optimization.

[Piedone]

Agree.