[Commerce] [Cart] Elements missing in the Xaml

[rajamatt]

1. Quantity of items in the cart can't be changed, the "More" and "Less" commands are never bound to in the Xaml
2. Items can't be removed from the cart because the "Remove" command is never bound to in the Xaml

see:

Uno.Samples/reference/Commerce/src/Commerce/Presentation/CartViewModel.cs

Lines 7 to 14 in bc73777

	public async ValueTask Remove(CartItem item, CancellationToken ct)
	=> await CartService.Remove(item.Product, ct);
	public async ValueTask More(CartItem item, CancellationToken ct)
	=> await CartService.Update(item.Product, item.Quantity + 1, ct);
	public async ValueTask Less(CartItem item, CancellationToken ct)
	=> await CartService.Update(item.Product, item.Quantity - 1, ct);

3. Number of items in cart is hardcoded

Uno.Samples/reference/Commerce/src/Commerce/Views/CartPage.xaml

Line 34 in bc73777

Text="3 Items"