[NF] Ceval/Simplify fixes.

- Fix simplification of division, result should always be Real.
- Fix ceval of integer with Integer argument.

Belonging to [master]:
  - #2108
  - OpenModelica/OpenModelica-testsuite#822

Compiler/NFFrontEnd/NFCeval.mo

@@ -751,6 +751,7 @@ function evalBuiltinInteger
   output Expression result;
 algorithm
   result := match arg
+    case Expression.INTEGER() then arg;
     case Expression.REAL() then Expression.INTEGER(realInt(arg.value));
     else algorithm printWrongArgsError(getInstanceName(), {arg}, sourceInfo()); then fail();
   end match;

Compiler/NFFrontEnd/NFSimplifyExp.mo

@@ -181,7 +181,7 @@ algorithm
         case Operator.ADD() then Expression.INTEGER(i1 + i2);
         case Operator.SUB() then Expression.INTEGER(i1 - i2);
         case Operator.MUL() then Expression.INTEGER(i1 * i2);
-        case Operator.DIV() then Expression.INTEGER(intDiv(i1, i2));
+        case Operator.DIV() then Expression.REAL(i1 / i2);
       end match;
 
     case Expression.BINARY(exp1=Expression.REAL(value=r1), exp2=Expression.REAL(value=r2))