Refactor freezing of JS objects

- Shallow-freezing of objects is never used in our codebase, so remove
   that code path.
 - Deep-freeze is bugged in recent versions of SpiderMonkey (see bug
   https://bugzilla.mozilla.org/show_bug.cgi?id=1930258). Until a fix
   and/or a better API is provided, reimplement this feature by
   recusively freezing object properties.
 - Add tests for the deepfreeze function.

source/ps/scripting/JSInterface_Mod.cpp

@@ -124,7 +124,7 @@ JS::Value GetEngineInfo(const ScriptInterface& scriptInterface)
 		 "engine_version", engine_version,
 		 "mods", mods);
 
-	Script::FreezeObject(rq, metainfo, true);
+	Script::DeepFreezeObject(rq, metainfo);
 
 	return metainfo;
 }