Previously we were returning a single view type id for all 'items' in collectionview, which meant if you were using a template selector, and had a variety of returned different DataTemplates, each would share the same recycled item.  When a recycled item is reused for a different template, it causes the view for that template to be recreated to be correct for the template selected.

This change returns a unique item id per DataTemplate.Type, so that recycled items should always have the correct DataTemplate.Type and not need to be recreated with a different view hierarchy.

Like on Android, we were using a single cell reuse identifier for iOS "items" regardless of if they had different DataTemplates.  If you were using a data template selector, and returned different data templates, whenever a recycled cell's data template didn't match the data template it needed to display for the new/recycled context, the whole view tree of that template would be recreated.

This change ensures we have a unique cell reuse id for every different DataTemplate.Type that might be returned by the template selector so that when a cell is recycled it should always be reused for the same Data Template it was created for, and so the view hierarchy won't be recreated.

This does require the DetermineCellReuseId to know the indexpath we're getting it for, so a new method was introduced, internal for NET7, protected for NET8+, and in NET8+ the old method is obsoleted.

…wAdapter.cs

Co-authored-by: E.Z. Hart <hartez@users.noreply.github.com>

…wAdapter.cs

Co-authored-by: Rui Marinho <me@ruimarinho.net>

…wAdapter.cs

Co-authored-by: Rui Marinho <me@ruimarinho.net>

The `CarouselViewAdapter` loops by basically returning a very large value for item count of its adapter/source which means the recyclerview is going to ask for view types with a position value that does not actually exist.

Previously this was ok because we returned only a single item view type ever, however now that we want to return a different type for template selector scenarios where there are potentially multiple template types, we need to override also the `GetItemViewType` and pass in the calculated position in the list properly (as we do in `OnBindViewHolder` here already) since the base `ItemsViewAdapter` class now calls `ItemsSource.GetItem(position)` in its `GetItemViewType()` call.