LYN-1818 | [USE CASE] Reparenting between different prefab instances by drag/drop in the Outliner (#1088)

* Add the last known parent to the prefab undo cache to detect changes in the owning instance.
Still WIP.

* Progress in handling reparenting. Still WIP, need a change in CreateLink that will be addressed in a separate branch and then merged back.

* A few fixes, reparenting now works with entities. Still working on instances.

* Fix assert crashing the Editor because of the arguments being in the wrong order.

* Handle moving the patches when removing and recreating links when reparenting nested instances.

* Rearrange some code to prevent including instance removal in instance update undo node, as it would be redundant and cause errors in some edge cases.

* Reorder instance reparenting to account for correct order of operation during undo/redo

* Fix order of operations to support multiple operations in one edit (reparenting to non-container entities while changing instance)

* Add function to refresh patches on links to allow aliases to be restored correctly on reparenting.

* Removed RefreshEntityPatchOnLink function. Introduced a simpler way of handling porting patches.

* Removing unnecessary code that was left after testing.

* Minor fixes to naming and comments.

* Restore previous error, no longer printing the failed patch.

* Remove unused includes.

* Restore include removed by mistake.

* Simplified patches retrieval by using internal function. Renamed some internal functions and variables to be more accurate.

Code/Framework/AzToolsFramework/AzToolsFramework/Prefab/PrefabUndoCache.cpp

@@ -73,14 +73,16 @@ namespace AzToolsFramework
             }
 
             PrefabDom oldData;
-            Retrieve(entityId, oldData);
+            AZ::EntityId oldParentId;
+            Retrieve(entityId, oldData, oldParentId);
 
             UpdateCache(entityId);
 
             PrefabDom newData;
-            Retrieve(entityId, newData);
+            AZ::EntityId newParentId;
+            Retrieve(entityId, newData, newParentId);
 
-            if (newData != oldData)
+            if (newData != oldData || oldParentId != newParentId)
             {
                 // display a useful message
                 AZ::Entity* entity = nullptr;
@@ -106,7 +108,7 @@ namespace AzToolsFramework
             // Clear out newly generated data and
             // replace with original data to ensure debug mode has the same data as profile/release
             // in the event of the consistency check failing.
-            m_entitySavedStates[entityId] = AZStd::move(oldData);
+            m_entitySavedStates[entityId] = {AZStd::move(oldData), oldParentId};
 
 #endif // ENABLE_UNDOCACHE_CONSISTENCY_CHECKS
         }
@@ -140,10 +142,13 @@ namespace AzToolsFramework
                 return;
             }
 
+            AZ::EntityId parentId;
+            AZ::TransformBus::EventResult(parentId, entityId, &AZ::TransformBus::Events::GetParentId);
+
             // Capture it
             PrefabDom entityDom;
             m_instanceToTemplateInterface->GenerateDomForEntity(entityDom, *entity);
-            m_entitySavedStates.emplace(AZStd::make_pair(entityId, AZStd::move(entityDom)));
+            m_entitySavedStates[entityId] = {AZStd::move(entityDom), parentId};
 
             AZLOG("Prefab Undo", "Correctly updated cache for entity of id %llu (%s)", static_cast<AZ::u64>(entityId), entity->GetName().c_str());
 
@@ -155,7 +160,7 @@ namespace AzToolsFramework
             m_entitySavedStates.erase(entityId);
         }
 
-        bool PrefabUndoCache::Retrieve(const AZ::EntityId& entityId, PrefabDom& outDom)
+        bool PrefabUndoCache::Retrieve(const AZ::EntityId& entityId, PrefabDom& outDom, AZ::EntityId& parentId)
         {
             auto it = m_entitySavedStates.find(entityId);
 
@@ -164,14 +169,15 @@ namespace AzToolsFramework
                 return false;
             }
 
-            outDom = AZStd::move(m_entitySavedStates[entityId]);
+            outDom = AZStd::move(m_entitySavedStates[entityId].dom);
+            parentId = m_entitySavedStates[entityId].parentId;
             m_entitySavedStates.erase(entityId);
             return true;
         }
 
-        void PrefabUndoCache::Store(const AZ::EntityId& entityId, PrefabDom&& dom)
+        void PrefabUndoCache::Store(const AZ::EntityId& entityId, PrefabDom&& dom, const AZ::EntityId& parentId)
         {
-            m_entitySavedStates.emplace(AZStd::make_pair(entityId, AZStd::move(dom)));
+            m_entitySavedStates[entityId] = {AZStd::move(dom), parentId};
         }
 
         void PrefabUndoCache::Clear()