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.h

@@ -52,6 +52,8 @@ namespace UnitTest
 
         AZStd::unique_ptr<ToolsTestApplication> CreateTestApplication() override;
 
+        void PropagateAllTemplateChanges();
+
         AZ::Entity* CreateEntity(const char* entityName, const bool shouldActivate = true);
 
         void CompareInstances(const Instance& instanceA, const Instance& instanceB, bool shouldCompareLinkIds = true,
@@ -62,6 +64,8 @@ namespace UnitTest
         //! Validates that all entities within a prefab instance are in 'Active' state.
         void ValidateInstanceEntitiesActive(Instance& instance);
 
+        void AddRequiredEditorComponents(AZ::Entity* entity);
+
         PrefabSystemComponent* m_prefabSystemComponent = nullptr;
         PrefabLoaderInterface* m_prefabLoaderInterface = nullptr;
         PrefabPublicInterface* m_prefabPublicInterface = nullptr;