ContainerType property implementations using improved syntax.

src/Avalonia.Controls/Generators/ItemContainerGenerator.cs

@@ -50,13 +50,7 @@ namespace Avalonia.Controls.Generators
         /// </summary>
         public IControl Owner { get; }
 
-        public virtual Type ContainerType
-        {
-            get
-            {
-                return null;
-            }
-        }
+        public virtual Type ContainerType => null;
 
         /// <inheritdoc/>
         public ItemContainerInfo Materialize(

src/Avalonia.Controls/Generators/ItemContainerGenerator`1.cs

@@ -35,13 +35,7 @@ namespace Avalonia.Controls.Generators
         }
 
         /// <inheritdoc/>
-        public override Type ContainerType
-        {
-            get
-            {
-                return typeof(T);
-            }
-        }
+        public override Type ContainerType => typeof(T);
 
         /// <summary>
         /// Gets the container's Content property.