A deep readonly typed version of given type T. Makes all properties or elements read only. It maps types using the following rules:

• arrays and tuples become readonly counterparts, and all element types are wrapped in Protected if applicable
• Maps of key type K and value type V become Maps of key type Protected<K> and value type Protected<V>
• Sets of element type E become Sets of element type Protected<E>
• Promises of value type E become Promises of value type Protected<E>
• Objects that have only simple properties (no functions or iterators) will have all the properties as Protected if applicable
• Any other type will not be mapped