JS scriptable objects are not properly overriding property attribute resolution

[pavelhoral]

This is related to mozilla/rhino#1558. I think we need to update our scriptable objects to implement IdScriptableObject#findInstanceIdInfo to have a working property attribute resolution (otherwise features like Object.assign won't work correctly).

[pavelhoral]

After some investigation the findInstanceIdInfo is probably not the solution nor the workaround we want. We should avoid using Object.assign in our scripts (and use lodash's _.assign) until we have a proper solution.

I would love to drop our custom ScriptableMap implementation and replace it with Rhino's NativaJavaMap. Unfortunately they are not compatible due to c094dcb which is a commit I am yet to fully understand 🙄