[iOS] Fixes crash in CollectionViews when using DataTemplateSelector as a DataTemplat...

[iOS] Fixes crash in CollectionViews when using DataTemplateSelector as a DataTemplate when used in GroupHeaders and or GroupFooters (#8674)

- fixes #8647

* Added repro and partial fix

* Removed some code in Templated cell to prevent an extension method being called twice.
Modified ItemsViewController to call different bind function. (Removed older one)
Added checks for Header/Footer in groupableItemsViewController.
Some code cleanup

* Removed unittest as I could not get it to run Due to missing Provisioningprofile

* Revert unintended change

* Cleanup some code