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>

src/Umbraco.Web.UI/Views/Partials/singleblock/default.cshtml

@@ -0,0 +1,9 @@
+@inherits Umbraco.Cms.Web.Common.Views.UmbracoViewPage<Umbraco.Cms.Core.Models.Blocks.BlockListItem>
+@{
+    if (Model.ContentKey == Guid.Empty) { return; }
+    var data = Model.Content;
+}
+@await Html.PartialAsync(
+    Html.SingleBlockPartialWithFallback("singleBlock/Components/" + data.ContentType.Alias,
+        "blocklist/Components/" + data.ContentType.Alias )
+    , Model)