Fixes: U4-6588 UmbracoSettings Error404 support Guids and Xpath - To achieve this, had to create an Id -> Key and Key -> Id method on EntityService including a cache for it which means updating all relavent cache refreshers to clear this cache when things are removed. Moved the logic for parsing an Umbraco XPath query (with tokens) to a stand-alone testable class (though haven't written tests), move the logic for looking up a not found page to the NotFoundHandlerHelper (instead of legacy 'library'). Fixes the $root query, since I don't think that ever worked. I've tested $root now for both MNTP and for the not found handler and it works.

src/Umbraco.Core/Configuration/InnerTextConfigurationElement.cs

@@ -34,7 +34,7 @@ namespace Umbraco.Core.Configuration
         {
             get
             {
-                var converted = ObjectExtensions.TryConvertTo<T>(RawValue);
+                var converted = RawValue.TryConvertTo<T>();
                 if (converted.Success == false)
                     throw new InvalidCastException("Could not convert value " + RawValue + " to type " + typeof(T));
                 return converted.Result;