fix to List.CartesianProduct node

[aparajit-pratap]

Purpose

Fixes regression caused by #9388 in List.CartesianProduct and adds missing test.

As a result of #9388 for loop behavior had changed. As a result of making Get.ValueAtIndex disallow array promotion of its list argument, for loops inside imperative language blocks no longer iterated over a single value. Previously the single value was getting promoted to an array before the for loop could iterate over it. This is because the for loop expression is first compiled to AST's as shown in this example:

                x = 0;
                a = [10, 20, 30, 40]
                for(val in a)
                {
                    x = x + val;
                }

                Compiles down to:

                x = 0;
                a = [10, 20, 30, 40];
                val = null;
                %forloop_key = a.key;
                %forloop_expr = a;

                while( %forloop_key != null)
                {
                    val = Get.ValueAtIndex(%forloop_expr, %forloop_key); => Array promotion!!!
                    %forloop_key = %forloop_key + 1;
                    x = x + val;
                }

The fix is to add yet another ValueAtIndex like ZT method specifically for for loop compilation that does not have the AllowArrayPromotion(false) attribute.

Declarations

Check these if you believe they are true

• The code base is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning, and are documented in the API Changes document.

Reviewers

@mjkkirschner
@QilongTang

FYIs

@smangarole

[aparajit-pratap]

@mjkkirschner I'm not happy with this solution of adding more ValueAtIndex methods just for the for loop but this is the simplest solution I have so far. Are you ok with it and the new method names or can you come up with better method names?