Move and update test assembly for Editor tests

Moved the test assembly definition to an Editor folder, renamed it to MackySoft.SerializeReferenceExtensions.Tests.Editor, and updated its root namespace. Added a placeholder TypeCandidateTestTypes.cs script for future Editor tests.

Author: mackysoft

Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Tests/Editor.meta

@@ -1,6 +1,6 @@
 {
-    "name": "Tests",
-    "rootNamespace": "",
+    "name": "MackySoft.SerializeReferenceExtensions.Tests.Editor",
+    "rootNamespace": "MackySoft.SerializeReferenceExtensions.Tests",
     "references": [
         "UnityEngine.TestRunner",
         "UnityEditor.TestRunner",

…erializeReferenceExtensions.Tests.asmdef …eReferenceExtensions.Tests.Editor.asmdefAssets/MackySoft/MackySoft.SerializeReferenceExtensions/Tests/MackySoft.SerializeReferenceExtensions.Tests.asmdef renamed to Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Tests/Editor/MackySoft.SerializeReferenceExtensions.Tests.Editor.asmdef Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Tests/MackySoft.SerializeReferenceExtensions.Tests.asmdef renamed to Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Tests/Editor/MackySoft.SerializeReferenceExtensions.Tests.Editor.asmdef

@@ -0,0 +1,8 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace MackySoft.SerializeReferenceExtensions.Tests
+{
+
+}