Bugfixes to enable slice-to-prefab conversion to run with less warnings/errors/crashes (#768)

While trying to process all slices and levels in Automated Testing, a few bugs came up that needed to be addressed:
- [LYN-3832] TransformComponent had a field removed without updating the version number and converter, which caused a lot of excessive warnings
- SliceComponent would crash in debug builds on instantiation failures due to a null dereference that was guarded against in most but not all places
- SliceConverter now detects when nested slices exist and gracefully warns about it.
- InstanceUpdateExecutor / TemplateInstanceMapper will now immediately remove instances that are unregistered, so that any in the queue don't get processed on a subsequent tick.  This was causing crashes when the instance was destroyed before the processing occurred.  It also has a side benefit of preventing the same instance from executing multiple times.
- Minor logic bugfix to the pack close warning, the boolean check was flipped.

Also added an early-out on SetTemplateId, since this was causing some unnecessary instance queue entries.

Code/Framework/AzToolsFramework/AzToolsFramework/ToolsComponents/TransformComponent.cpp

@@ -162,6 +162,12 @@ namespace AzToolsFramework
                     classElement.RemoveElementByName(AZ_CRC("InterpolateScale", 0x9d00b831));
                 }
 
+                if (classElement.GetVersion() < 10)
+                {
+                    // The "Sync Enabled" flag is no longer needed.
+                    classElement.RemoveElementByName(AZ_CRC_CE("Sync Enabled"));
+                }
+
                 return true;
             }
         } // namespace Internal
@@ -1305,7 +1311,7 @@ namespace AzToolsFramework
                     Field("IsStatic", &TransformComponent::m_isStatic)->
                     Field("InterpolatePosition", &TransformComponent::m_interpolatePosition)->
                     Field("InterpolateRotation", &TransformComponent::m_interpolateRotation)->
-                    Version(9, &Internal::TransformComponentDataConverter);
+                    Version(10, &Internal::TransformComponentDataConverter);
 
                 if (AZ::EditContext* ptrEdit = serializeContext->GetEditContext())
                 {