[iOS] Fixed crash displaying strings in CarouselView (#7858)

* Added repro sample

* Fixed the crash on DequeueReusableCell registering the correct cell types

* Added instructions to the test

* Fixed wrong paths on Controls Issues projitems

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7789.xaml

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<controls:TestContentPage xmlns="http://xamarin.com/schemas/2014/forms"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
+             xmlns:controls="clr-namespace:Xamarin.Forms.Controls"
+             mc:Ignorable="d"
+             x:Class="Xamarin.Forms.Controls.Issues.Issue7789">
+    <ContentPage.Content>
+    <StackLayout Margin="10">
+        <Label
+            Text="If the CarouselView below is rendered without problems, the test passes."/>
+        <CarouselView
+            BackgroundColor="GreenYellow">
+            <CarouselView.ItemsSource>
+                <x:Array Type="{x:Type x:String}">
+                    <x:String>Baboon</x:String>
+                    <x:String>Capuchin Monkey</x:String>
+                    <x:String>Blue Monkey</x:String>
+                    <x:String>Squirrel Monkey</x:String>
+                    <x:String>Golden Lion Tamarin</x:String>
+                    <x:String>Howler Monkey</x:String>
+                    <x:String>Japanese Macaque</x:String>
+                    <x:String>Mandrill</x:String>
+                    <x:String>Proboscis Monkey</x:String>
+                    <x:String>Red-shanked Douc</x:String>
+                    <x:String>Gray-shanked Douc</x:String>
+                    <x:String>Golden Snub-nosed Monkey</x:String>
+                    <x:String>Black Snub-nosed Monkey</x:String>
+                    <x:String>Tonkin Snub-nosed Monkey</x:String>
+                    <x:String>Thomas's Langur</x:String>
+                    <x:String>Purple-faced Langur</x:String>
+                    <x:String>Gelada</x:String>
+                </x:Array>
+            </CarouselView.ItemsSource>
+        </CarouselView>
+    </StackLayout> 
+    </ContentPage.Content>
+</controls:TestContentPage>

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Issue7789.xaml.cs

@@ -0,0 +1,38 @@
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+using Xamarin.Forms.Xaml;
+using System.Collections.Generic;
+
+#if UITEST
+using Xamarin.UITest;
+using Xamarin.UITest.Queries;
+using NUnit.Framework;
+using Xamarin.Forms.Core.UITests;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[NUnit.Framework.Category(UITestCategories.CollectionView)]
+#endif
+#if APP
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.Github, 7789, "CarouselView crash when displaying strings", PlatformAffected.iOS)]
+	public partial class Issue7789 : TestContentPage
+	{
+		public Issue7789()
+		{
+#if APP
+			Device.SetFlags(new List<string> { CollectionView.CollectionViewExperimental });
+			InitializeComponent();
+#endif
+		}
+
+		protected override void Init()
+		{
+
+		}
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -61,6 +61,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue7593.xaml.cs">
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="$(MSBuildThisFileDirectory)Issue7789.xaml.cs">
+      <SubType>Code</SubType>
+    </Compile>
     <Compile Include="$(MSBuildThisFileDirectory)RefreshViewTests.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue7338.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ScrollToGroup.cs" />
@@ -1407,7 +1410,10 @@
     <Compile Update="$(MSBuildThisFileDirectory)Issue7357.xaml.cs">
       <DependentUpon>Issue7357.xaml</DependentUpon>
     </Compile>
-    <Compile Update="C:\Users\hartez\Documents\Xamarin\Xamarin.Forms\Xamarin.Forms.Controls.Issues\Xamarin.Forms.Controls.Issues.Shared\Issue7519Xaml.xaml.cs">
+    <Compile Update="$(MSBuildThisFileDirectory)Issue7789.xaml.cs">
+      <DependentUpon>Issue7789.xaml</DependentUpon>
+    </Compile>
+    <Compile Update="$(MSBuildThisFileDirectory)Issue7519Xaml.xaml.cs">
       <DependentUpon>Issue7519Xaml.xaml</DependentUpon>
     </Compile>
     <Compile Update="$(MSBuildThisFileDirectory)Issue5354.xaml.cs">
@@ -1492,4 +1498,10 @@
       <Generator>MSBuild:Compile</Generator>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <EmbeddedResource Include="$(MSBuildThisFileDirectory)Issue7789.xaml">
+      <SubType>Designer</SubType>
+      <Generator>MSBuild:Compile</Generator>
+    </EmbeddedResource>
+  </ItemGroup>
 </Project>

Xamarin.Forms.Platform.iOS/CollectionView/CarouselViewController.cs

@@ -60,6 +60,7 @@ namespace Xamarin.Forms.Platform.iOS
 		protected override void RegisterViewTypes()
 		{
 			CollectionView.RegisterClassForCell(typeof(CarouselTemplatedCell), CarouselTemplatedCell.ReuseId);
+			base.RegisterViewTypes();
 		}
 
 		internal void TearDown()