Grow DynSem with knowledge of arrays

[vvergu]

Any serious programming language has arrays but there is currently no (efficient) way to specify semantics of languages with arrays in DynSem. This problem should be resolved by adding arrays as built-in types in DynSem.

[eelcovisser]

It would be good to think about the design of arrays. In a sense, we already have arrays: maps provide association between index and value. So, from that perspective, we don't need arrays. And even the notation is already array-like. I understand that we need a more array-like implementation to get performance. But perhaps that is just a matter of an annotation on the map type alias declaration.