[arrays]: Array outer dimension requires array storage ordering definition

[steleman]

What is the expected enhancement?

The OpenQASM3 Spec for Arrays contains the following statement:

The subscript operator [] is used for element access, and for multi-dimensional
arrays subarray accesses can be specified using a comma-delimited list of indices
(e.g. myArr[1, 2, 3]), _with the outer dimension specified first_.

https://openqasm.com/language/types.html#arrays

The reference to an array's outer dimension is ambiguous, because the current Spec does not define the storage ordering for Arrays. The memory contents of an array's outer dimension is dependent on the array's storage ordering.

Proposed remedy:

OpenQASM3 arrays shall be stored in Row Major order.

There are subtle implications when deciding the storage ordering for Arrays. The Row Major ordering provides optimization advantages to the compiler that are not available with Column Major ordering.

[jwoehr]

I'm going to wait to hear from the TSC before attempting to turn this Issue into a Pull Request.