Adapt 0 A.D. to SpiderMonkey ESR 102

This follows the migration guide at:
https://github.com/mozilla-spidermonkey/spidermonkey-embedding-examples

Based on patch by: wraitii
Differential Revision: https://code.wildfiregames.com/D5002

source/simulation2/scripting/EngineScriptConversions.cpp

@@ -1,4 +1,4 @@
-/* Copyright (C) 2023 Wildfire Games.
+/* Copyright (C) 2024 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -62,7 +62,7 @@ template<> void Script::ToJSVal<IComponent*>(const ScriptRequest& rq,  JS::Mutab
 		return;
 	}
 
-	JS::SetPrivate(obj, static_cast<void*>(val));
+	JS::SetReservedSlot(obj, ScriptInterface::JSObjectReservedSlots::PRIVATE, JS::PrivateValue(val));
 	ret.setObject(*obj);
 }