[NF] Constant evaluation optimizations.

- Added a field to NFExpression.ARRAY that indicates whether an array
  contains only literal expression or not, so that arrays that have
  already been evaluated can be skipped during constant evaluation.
- Implemented Ceval.evalExpPartial that only evaluates the parts of an
  expression that can be evaluated, keeping e.g. iterators intact.
- Use the function mentioned above to optimize the evaluation of array
  constructors and reductions, by partially evaluating the expression
  that's evaluated in each iteration.

Belonging to [master]:
  - #2812

Author: perost

Compiler/NFFrontEnd/NFBuiltinCall.mo

@@ -200,7 +200,7 @@ public
       fail();
     end if;
 
-    arrayExp := Expression.ARRAY(Type.UNKNOWN(), posArgs);
+    arrayExp := Expression.makeArray(Type.UNKNOWN(), posArgs);
   end makeArrayExp;
 
   function makeCatExp