#3526907 Send timestamp, autoSave hash and unique client id with post and patch...

For both POST and PATCH requests to /layout/{entity_type}/{entity_id} I am appending a timestamp, the last received autoSave hash and unique client id in the payload.

When a request is received that contains a new autoSaves hash, it's stored in the Redux store to be sent with the subsequent request.

Next, I think the backend needs to take the clientInstanceId and timestamp and use them to be more clever about when it's returning a conflict error.

I have attempted to centralise the error handling from requests to the above however I'm not sure the implementation is flexible enough - I suspect errors now are TOO intrusive for some errors. Now the error completely hides the UI and forces the user to refresh to recover for any error on these endpoints - where previously some errors could be recovered from with an "undo latest action" button. This needs work still.

modules/xb_personalization/src/Entity/Segment.php

@@ -97,7 +97,7 @@ final class Segment extends ConfigEntityBase implements SegmentInterface {
   /**
    * The condition plugin manager for instantiating the segmentation rules.
    */
-  protected (ExecutableManagerInterface&FilteredPluginManagerInterface)|null $conditionPluginManager;
+  protected (ExecutableManagerInterface&FilteredPluginManagerInterface)|NULL $conditionPluginManager;
 
   /**
    * {@inheritdoc}