[iOS] Fix cell size changed on CollectionView

[rmarinho]

Description of Change

CollectionView Cells need a way to know that the contents of the MAUI view have changed and to update it's layout. We used MeasuredInvalidated for that, but the new layouts weren't bubbling it from the children, this pr allows that to done when a child is added to the VE.

On iOS the InvalidateLayout wasn0't working to update cell size, but if we reload the visible cells it works fine.

Issues Fixed

Fixes #3643

Use this to test

<Grid>
      <CollectionView ItemsSource="{Binding Items}" BackgroundColor="Pink" >
          <CollectionView.ItemTemplate>
              <DataTemplate>
                  <Grid BackgroundColor="Red" Padding="10">
                      <Label Text="{Binding Name}" BackgroundColor="Yellow" TextColor="Black"/>
                  </Grid>
              </DataTemplate>
          </CollectionView.ItemTemplate>
      </CollectionView>
 </Grid>

public MainPage()
{
   InitializeComponent();
   BindingContext = this;
   Device.StartTimer(TimeSpan.FromSeconds(5), () =>
   {
   	UpdateStuff();
   	return false;
   });
}

ObservableCollection<SomeItem> _items;
public ObservableCollection<SomeItem> Items
{
   get
   {
   	if (_items == null)
   	{
   		_items = new ObservableCollection<SomeItem>(Enumerable.Range(0, 1).Select(c =>
   		{
   			return new SomeItem() { Name = string.Format("Item {0}", c) };
   		}));
   	}

   	return _items;
   }
}
   
void UpdateStuff()
{
   System.Diagnostics.Debug.WriteLine($"UpdateStuff");
   		var bigString = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
   foreach (var item in Items)
   {
   	item.Name = bigString;
   }
}

public class SomeItem : INotifyPropertyChanged
{
   string name;
   public string Name
   {
   	get => name;
   	set
   	{
   		name = value;
   		PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Name)));
   	}
   }

   public event PropertyChangedEventHandler PropertyChanged;
}

[jsuarezruiz]

/azp run

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