[C] alias shell names (#5624)

* [C] alias shell names

* - change from ShellTab to Tab

Xamarin.Forms.Core/Shell/Shell.cs

@@ -12,7 +12,7 @@ using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
-	[ContentProperty("Items")]
+	[ContentProperty(nameof(Items))]
 	public class Shell : Page, IShellController, IPropertyPropagationController
 	{
 		public static readonly BindableProperty BackButtonBehaviorProperty =
@@ -640,6 +640,7 @@ namespace Xamarin.Forms
 		}
 
 		public ShellItemCollection Items => (ShellItemCollection)GetValue(ItemsProperty);
+		public ShellItemCollection Flyout => Items;
 
 		public DataTemplate ItemTemplate {
 			get => (DataTemplate)GetValue(ItemTemplateProperty);

Xamarin.Forms.Core/Shell/ShellContent.cs

@@ -12,7 +12,11 @@ using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
-	[ContentProperty("Content")]
+	public class TabContent : ShellContent
+	{
+	}
+
+	[ContentProperty(nameof(Content))]
 	public class ShellContent : BaseShellItem, IShellContentController
 	{
 		static readonly BindablePropertyKey MenuItemsPropertyKey =

Xamarin.Forms.Core/Shell/ShellItem.cs

@@ -7,7 +7,12 @@ using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
-	[ContentProperty("Items")]
+	public class FlyoutItem : ShellItem
+	{
+		public ShellSectionCollection Tabs => Items;
+	}
+
+	[ContentProperty(nameof(Items))]
 	public class ShellItem : ShellGroupItem, IShellItemController, IElementConfiguration<ShellItem>, IPropertyPropagationController
 	{
 		#region PropertyKeys

Xamarin.Forms.Core/Shell/ShellSection.cs

@@ -8,7 +8,12 @@ using Xamarin.Forms.Internals;
 
 namespace Xamarin.Forms
 {
-	[ContentProperty("Items")]
+	public class Tab : ShellSection
+	{
+		public ShellContentCollection Content => Items;
+	}
+
+	[ContentProperty(nameof(Items))]
 	public class ShellSection : ShellGroupItem, IShellSectionController, IPropertyPropagationController
 	{
 		#region PropertyKeys