Changes all collections from collection builders to resolve the concrete instances lazily.

This means we don't have to inject Lazy<T> all over the place when dealing with
colleciton builders and circular references since this will automatically just work OOTB.
This in theory should also allocate less instances during startup.

src/Umbraco.Core/Composing/BuilderCollectionBase.cs

@@ -1,43 +1,34 @@
-using System.Collections;
+using System;
+using System.Collections;
 using System.Collections.Generic;
-using System.Linq;
 
 namespace Umbraco.Cms.Core.Composing
 {
+
     /// <summary>
     /// Provides a base class for builder collections.
     /// </summary>
     /// <typeparam name="TItem">The type of the items.</typeparam>
     public abstract class BuilderCollectionBase<TItem> : IBuilderCollection<TItem>
     {
-        private readonly TItem[] _items;
+        private readonly LazyReadOnlyCollection<TItem> _items;
 
-        /// <summary>
         /// Initializes a new instance of the <see cref="BuilderCollectionBase{TItem}"/> with items.
         /// </summary>
         /// <param name="items">The items.</param>
-        protected BuilderCollectionBase(IEnumerable<TItem> items)
-        {
-            _items = items.ToArray();
-        }
+        public BuilderCollectionBase(Func<IEnumerable<TItem>> items) => _items = new LazyReadOnlyCollection<TItem>(items);
 
         /// <inheritdoc />
-        public int Count => _items.Length;
+        public int Count => _items.Count;
 
         /// <summary>
         /// Gets an enumerator.
         /// </summary>
-        public IEnumerator<TItem> GetEnumerator()
-        {
-            return ((IEnumerable<TItem>) _items).GetEnumerator();
-        }
+        public IEnumerator<TItem> GetEnumerator() => ((IEnumerable<TItem>)_items).GetEnumerator();
 
         /// <summary>
         /// Gets an enumerator.
         /// </summary>
-        IEnumerator IEnumerable.GetEnumerator()
-        {
-            return GetEnumerator();
-        }
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
     }
 }