Fixes: #U4-894 - moves the int Priority out of the IThumbnailProvider class as it is only metadata, moved

this into a new generic WeightedPluginAttribute which can be used for other resolves/objects that require a weight.

src/Umbraco.Core/ObjectResolution/WeightedPluginAttribute.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace Umbraco.Core.ObjectResolution
+{
+	/// <summary>
+	/// Some many object resolvers require that the objects that they resolve have weights applied to them so that
+	/// the objects are returned in a sorted order, this attribute is used in these scenarios.
+	/// </summary>
+	[AttributeUsage(AttributeTargets.Class, AllowMultiple = false)]
+	internal class WeightedPluginAttribute : Attribute
+	{
+		public WeightedPluginAttribute(int weight)
+		{
+			Weight = weight;
+		}
+
+		public int Weight { get; private set; }
+	}
+}