What's the API to construct an array of unsinkable elements

I'm not sure what the array constructor should look like.

A constructor for `A` has a signature `(T1, ..., Tn) -> A`, suggesting that `A` is sinkable (otherwise it could not be returned). What's a good pattern to initialize unsinkable things in an array?

Start by reading the issue's discussion of array constructors, the signature `(T1, ..., Tn) -> A`, and the distinction between sinkable and unsinkable values. No source files, tests, or entry points are named, so first locate the array API and ownership or sinkability rules in the prototype. Done means agreeing on and documenting an API pattern for initializing arrays of unsinkable elements.

Written by the indexing model from the issue text.