CR: Make DefaultComponentActivator internal

Author: SteveSandersonMS

src/Components/Components/ref/Microsoft.AspNetCore.Components.netcoreapp.cs

@@ -107,11 +107,6 @@ protected virtual void OnParametersSet() { }
         protected virtual bool ShouldRender() { throw null; }
         protected void StateHasChanged() { }
     }
-    public partial class DefaultComponentActivator : Microsoft.AspNetCore.Components.IComponentActivator
-    {
-        public DefaultComponentActivator() { }
-        public Microsoft.AspNetCore.Components.IComponent CreateInstance(System.Type componentType) { throw null; }
-    }
     public abstract partial class Dispatcher
     {
         protected Dispatcher() { }

src/Components/Components/src/DefaultComponentActivator.cs

@@ -5,15 +5,9 @@
 
 namespace Microsoft.AspNetCore.Components
 {
-    /// <summary>
-    /// Default implementation of <see cref="IComponentActivator"/>.
-    /// </summary>
-    public class DefaultComponentActivator : IComponentActivator
+    internal class DefaultComponentActivator : IComponentActivator
     {
-        // If no IComponentActivator is supplied by DI, the renderer uses this instance.
-        // It's internal because in the future, we might want to add per-scope state and then
-        // it would no longer be applicable to have a shared instance.
-        internal static IComponentActivator Instance { get; } = new DefaultComponentActivator();
+        public static IComponentActivator Instance { get; } = new DefaultComponentActivator();
 
         /// <inheritdoc />
         public IComponent CreateInstance(Type componentType)