ForLoopsLowering: Reduce unnecessary temporary variables for the

"checked step" (check for a positive step arg) and "negated step"
(negate the step arg when the nested step is negative).

compiler/testData/codegen/bytecodeText/forLoop/stepped/stepOneThenStepOne.kt

@@ -14,12 +14,11 @@ fun box(): String {
 //   // Standard form of loop over progression
 //   var inductionVar = 1
 //   val last = 4
-//   val step = 1
 //   if (inductionVar <= last) {
 //     // Loop is not empty
 //     do {
 //       val i = inductionVar
-//       inductionVar += step
+//       inductionVar += 1
 //       // Loop body
 //     } while (inductionVar <= last)
 //   }