Use SafeArea in the Samples App

[kazo0]

We should be using the SafeArea in the Shell, rather than doing things like this:

uno.toolkit.ui/samples/Uno.Toolkit.Samples/Uno.Toolkit.Samples.Shared/Shell.xaml.cs

Lines 85 to 101 in 80ebae8

	/// <summary>
	/// This method handles the top padding for phones like iPhone X.
	/// </summary>
	private void InitializeSafeArea()
	{
	#if !IS_WINUI
	var full = XamlWindow.Current.Bounds;
	var bounds = Windows.UI.ViewManagement.ApplicationView.GetForCurrentView().VisibleBounds;
	var topPadding = Math.Abs(full.Top - bounds.Top);
	if (topPadding > 0)
	{
	TopPaddingRow.Height = new GridLength(topPadding);
	}
	#endif
	}

We should also be making sure the app content, including the runtime test runner page, all stay within the bounds of the safe area

[carlh98]

@kazo0 when this PR is merged #616
We'll be able to close this issue