Support for instance arrays

[eschkufz]

Overview

Arrays of module instantiations actually look A LOT like generate statements. I guess that's not surprising since we handle instantiations and generates nearly identically everywhere else.

Deliverables

• Add parser support for instance arrays
• Add typechecking support for instance arrays
• TEMPORARY --- Emit typechecker errors for instance array usage
• Support for instance arrays
• FINAL --- Turn off typechecker errors and switch to support

[eschkufz]

Merging these changes back into master to prevent the use of array instances while work on this ticket continues.