Fixes: U4-4926 Pre-values need to be cloned in/out of the cache

Conflicts:
	src/Umbraco.Core/Models/PreValue.cs
	src/Umbraco.Core/Models/PreValueCollection.cs

src/Umbraco.Core/Models/PreValue.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Represents a stored pre-value field value
     /// </summary>
-    public class PreValue
+    public class PreValue : IDeepCloneable
     {
         public PreValue(int id, string value)
         {
@@ -25,5 +25,12 @@
         /// The database id for the pre-value field value
         /// </summary>
         public int Id { get; private set; }
+
+        public virtual object DeepClone()
+        {
+            //Memberwise clone on PreValue will work since it doesn't have any deep elements
+            var clone = (PreValue)MemberwiseClone();            
+            return clone;
+        }
     }
 }

src/Umbraco.Core/Models/PreValueCollection.cs

@@ -14,7 +14,7 @@ namespace Umbraco.Core.Models
     /// Most legacy property editors won't support the dictionary format but new property editors should always use the dictionary format.
     /// In order to get overrideable pre-values working we need a dictionary since we'll have to reference a pre-value by a key.
     /// </remarks>
-    public class PreValueCollection
+    public class PreValueCollection : IDeepCloneable
     {
         private IDictionary<string, PreValue> _preValuesAsDictionary;
         private IEnumerable<PreValue> _preValuesAsArray;
@@ -82,5 +82,21 @@ namespace Umbraco.Core.Models
             }
             return result;
         }
+
+        public object DeepClone()
+        {
+            var clone = (PreValueCollection) MemberwiseClone();
+            if (_preValuesAsArray != null)
+            {
+                clone._preValuesAsArray = _preValuesAsArray.Select(x => (PreValue)x.DeepClone()).ToArray();    
+            }
+            if (_preValuesAsDictionary != null)
+            {
+                clone._preValuesAsDictionary = _preValuesAsDictionary.ToDictionary(x => x.Key, x => (PreValue)x.Value.DeepClone());    
+            }
+            
+
+            return clone;
+        }
     }
 }

src/Umbraco.Core/Persistence/Repositories/DataTypeDefinitionRepository.cs

@@ -295,8 +295,8 @@ AND umbracoNode.id <> @id",
                 var cached = _cacheHelper.RuntimeCache.GetCacheItemsByKeySearch<PreValueCollection>(GetPrefixedCacheKey(dataTypeId));
                 if (cached != null && cached.Any())
                 {
-                    //return from the cache
-                    return cached.First();
+                    //return from the cache, ensure it's a cloned result
+                    return (PreValueCollection)cached.First().DeepClone();
                 }
 
                 l.UpgradeToWriteLock();