Feature: single block property editor (#20098)

* First Go at the single block property editor based on blocklistpropertyeditor

* Add simalar tests to the blocklist editor

Also check whether either block of configured blocks can be picked and used from a data perspective

* WIP singleblock Valiation tests

* Finished first full pass off SingleBlock validation testing

* Typos, Future test function

* Restore accidently removed file

* Introduce propertyValueConverter

* Comment updates

* Add singleBlock renderer

* Textual improvements

Comment improvements, remove licensing in file

* Update DataEditorCount by 1 as we introduced a new one

* Align test naming

* Add ignored singleblock default renderer

* Enable SingleBlock Property Indexing

* Enable Partial value merging

* Fix indentation

---------

Co-authored-by: kjac <kja@umbraco.dk>

tests/Umbraco.Tests.UnitTests/Umbraco.Core/Composing/TypeLoaderTests.cs

@@ -132,7 +132,7 @@ public class TypeLoaderTests
     public void GetDataEditors()
     {
         var types = _typeLoader.GetDataEditors();
-        Assert.AreEqual(36, types.Count());
+        Assert.AreEqual(37, types.Count());
     }
 
     /// <summary>