Add Trait to write an 'OpaqueView' to the TES which makes the underlying object inaccessible

Provide the ability to write an object into the TES that for all intents and purposes is unreadable. Useful in case it is eg. purely the 'backing store' for a view, and the original should never be accessed directly, and only through the separately written view. Possible use-cases for this are the ability to write multiple views all using the same backing store -- which cannot be achieved using writeViewFor, which assumes a one-to-one-invertible relation between view and backing store. Also allows for views which cannot be automatically constructed from their backing store as required by writeViewFor, in which case a dedicate view can be created and stored, separately from the backing store which can be hidden behind an opaqueView.