Fix several Prefab outliner ordering issues (#5747)

* Fix several Prefab outliner ordering issues

This change does a few things to address instability in entity order when prefabs are enabled:
- Changes ordering behavior on entity add to always be "insert after the last selected sibling of the new entity, or at the end if there is no selected sibling"
- Adds some logic to ensure selection stays frozen during prefab propagation to allow this behavior to be used
- Alters delta generation in `PrefabPublicHandler::CreateEntity` to use the template instead of reserializing the DOM - this avoids a whole bunch of patching issues caused by EditorEntitySortComponent doing post-hoc order fix-up and should generally be safer/faster as we're producing patches for the actual target for those patches
- Because the duplicate action is DOM-driven, and there's some thorniness around making changes that will affect the template during propagation, this adds `PrefabPublicHandler::AddNewEntityToSortOrder` to directly patch the DOM for the duplicate case

Two bits of this come from patches from the incredibly helpful @AMZN-daimini
- Alters `PrefabPublicHandler::GenerateUndoNodesForEntityChangeAndUpdateCache` behavior for determining what's an override: we now check to see if we're part of the current focused instance but *not* owned by the focus instance directly. This lets entity order for nested prefabs get saved to the owning prefab instead of as an override. I'm putting this up for discussion without a feature flag gating it, but we may wish to make this a toggle or disable it outright for stabilization (in which case entity order won't be saved to the owning prefab)
- Adds a custom serializer for EditorEntitySortComponent. This isn't strictly necessary now, but it was very useful for debugging and ended up receiving much more manual testing its migration path and save/load path more than I've tested without using the serializer.

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Add missing serializers

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Address some review feedback

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Generate patch in `PrefabPublicHandler::CreateEntity` using the instance's fully evaluated template in-memory

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Fix up comment

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Fix Linux build

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Try to make test less timing dependent (haven't been able to repro failure locally)

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Fix another build issue

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Fix unit test failures

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* Fix a duplicate issue with sanitization that was causing sporadic test failure (thanks, test!)

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

* One more Linux fix...

Signed-off-by: Nicholas Van Sickle <nvsickle@amazon.com>

AutomatedTesting/Gem/PythonTests/editor/EditorScripts/EntityOutliner_EntityOrdering.py

@@ -95,7 +95,8 @@ def EntityOutliner_EntityOrdering():
         entity_outliner_model.dropMimeData(
             mime_data, QtCore.Qt.MoveAction, target_row, 0, target_index.parent()
         )
-        QtWidgets.QApplication.processEvents()
+        # Wait after move to let events (i.e. prefab propagation) process
+        general.idle_wait(1.0)
 
     # Move an entity before another entity in the order by dragging the source above the target
     move_entity_before = lambda source_name, target_name: _move_entity(
@@ -119,24 +120,24 @@ def EntityOutliner_EntityOrdering():
 
         # Our new entity should be given a name with a number automatically
         new_entity = f"Entity{i+1}"
-        # The new entity should be added to the top of its parent entity
-        expected_order = [new_entity] + expected_order
+        # The new entity should be added to the bottom of its parent entity
+        expected_order = expected_order + [new_entity]
 
         verify_entities_sorted(expected_order)
 
-    # 3) Move "Entity1" to the top of the order
-    move_entity_before("Entity1", "Entity5")
-    expected_order = ["Entity1", "Entity5", "Entity4", "Entity3", "Entity2"]
+    # 3) Move "Entity5" to the top of the order
+    move_entity_before("Entity5", "Entity1")
+    expected_order = ["Entity5", "Entity1", "Entity2", "Entity3", "Entity4"]
     verify_entities_sorted(expected_order)
 
-    # 4) Move "Entity4" to the bottom of the order
-    move_entity_after("Entity4", "Entity2")
-    expected_order = ["Entity1", "Entity5", "Entity3", "Entity2", "Entity4"]
+    # 4) Move "Entity2" to the bottom of the order
+    move_entity_after("Entity2", "Entity4")
+    expected_order = ["Entity5", "Entity1", "Entity3", "Entity4", "Entity2"]
     verify_entities_sorted(expected_order)
 
     # 5) Add another new entity, ensure the rest of the order is unchanged
     create_entity()
-    expected_order = ["Entity6", "Entity1", "Entity5", "Entity3", "Entity2", "Entity4"]
+    expected_order = ["Entity5", "Entity1", "Entity3", "Entity4", "Entity2", "Entity6"]
     verify_entities_sorted(expected_order)