Provides an abstraction for creating the JavaScriptEncoder used in SystemTextConfigurationEditorJsonSerializer (#19849)

* Provides an abstraction for creating the JavaScriptEncoder used in SystemTextConfigurationEditorJsonSerializer.

* Generalised JSON serialization encoder factory to work for all System.Tex.Json serializers.
Added the serializer's name as a parameter to allow for different encodings per serializer if required.

* Fixed tests by removing use of obsolete constructors.

* Removed name parameter and used a generic type instead.

tests/Umbraco.TestData/UmbracoTestDataController.cs

@@ -299,7 +299,7 @@ public class UmbracoTestDataController : SurfaceController
             throw new InvalidOperationException($"No {editorAlias} editor found");
         }
 
-        var serializer = new SystemTextConfigurationEditorJsonSerializer();
+        var serializer = new SystemTextConfigurationEditorJsonSerializer(new DefaultJsonSerializerEncoderFactory());
 
         dt = new DataType(editor, serializer)
         {