dyno: materialize promoted and iterable expressions into arrays when assigned to variables or returned from procedures

[DanilaFe]

In production, writing:

var A = foreach i in 1..10 do i*i;

Creates a new array A that's populated with the results of the iterable. In Dyno, currently, it gives A an IterableType (not an array). I believe converting iterables to arrays in such cases is an explicit design choice, and thus, we ought to replicate it in Dyno.

[bradcray]

Note that there are three similar-but-different cases in the production compiler for this pattern. In the one, the index set of the RHS is preserved and used to establish the array's domain. Like in this case, A would be over [1..10]. In the second, when we're iterating over a domain or an array, the new array's domain matches the iterand's. In the third case—say we're invoking an iterator that yields integers read from a file until it hits EOF—the array is 1D, 0-based, and its size is only determined at the time of its creation.

I believe Vass is most familiar with the first two cases and how they are implemented / what we use today to query whether the index set of an iterable is well-known / should be treated as the domain.