Prefab/unit tests for deletion (#6034)

* Added tests for deleting entity under level and other prefabs

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

* Added class comments and improved variable names

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

* Called the reflect function of PrefabFocusHandler from PrefabSystemComponent

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

* Added couple of unit tests around entity and prefab deletion

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

* Used engine root path from settings registry as fake path for prefab creation

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

* Added 2 unit tests around deleting prefabs

Signed-off-by: srikappa-amzn <82230713+srikappa-amzn@users.noreply.github.com>

Code/Framework/AzToolsFramework/Tests/Prefab/PrefabTestFixture.cpp

@@ -57,6 +57,11 @@ namespace UnitTest
         return AZStd::make_unique<PrefabTestToolsApplication>("PrefabTestApplication");
     }
 
+    void PrefabTestFixture::PropagateAllTemplateChanges()
+    {
+        m_prefabSystemComponent->OnSystemTick();
+    }
+
     AZ::Entity* PrefabTestFixture::CreateEntity(const char* entityName, const bool shouldActivate)
     {
         // Circumvent the EntityContext system and generate a new entity with a transformcomponent
@@ -125,4 +130,13 @@ namespace UnitTest
             EXPECT_EQ(entityInInstance->GetState(), AZ::Entity::State::Active);
         }
     }
+
+    void PrefabTestFixture::AddRequiredEditorComponents(AZ::Entity* entity)
+    {
+        ASSERT_TRUE(entity != nullptr);
+        entity->Deactivate();
+        AzToolsFramework::EditorEntityContextRequestBus::Broadcast(
+            &AzToolsFramework::EditorEntityContextRequests::AddRequiredComponents, *entity);
+        entity->Activate();
+    }
 }