While loop implementation && first loop test

compiler/testData/ir/irCfg/loop/factorial.kt

@@ -0,0 +1,7 @@
+fun factorial(i: Int): Int {
+    var result = 1
+    for (j in 2..i) {
+        result *= j
+    }
+    return result
+}

compiler/testData/ir/irCfg/loop/factorial.txt

@@ -0,0 +1,40 @@
+// FILE: /factorial.kt
+// FUN: factorial
+BB 0
+CONTENT
+      1 FUN public fun factorial(i: kotlin.Int): kotlin.Int
+      2 CONST Int type=kotlin.Int value='1'
+      3 VAR var result: kotlin.Int
+      4 CALL 'iterator(): IntIterator' type=kotlin.collections.IntIterator origin=FOR_LOOP_ITERATOR
+      5 VAR IR_TEMPORARY_VARIABLE val tmp0_iterator: kotlin.collections.IntIterator
+      6 WHILE label=null origin=FOR_LOOP_INNER_WHILE
+OUTGOING -> BB 1
+    While entry: WHILE label=null origin=FOR_LOOP_INNER_WHILE
+BB 1
+INCOMING <- BB 0, 2
+    While entry: WHILE label=null origin=FOR_LOOP_INNER_WHILE
+CONTENT
+OUTGOING -> BB 2, 3
+    CALL 'hasNext(): Boolean' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
+BB 2
+INCOMING <- BB 1
+    CALL 'hasNext(): Boolean' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
+CONTENT
+      1 CALL 'next(): Int' type=kotlin.Int origin=FOR_LOOP_NEXT
+      2 VAR val j: kotlin.Int
+      3 SET_VAR 'result: Int' type=kotlin.Unit origin=MULTEQ
+OUTGOING -> BB 1
+    While entry: WHILE label=null origin=FOR_LOOP_INNER_WHILE
+BB 3
+INCOMING <- BB 1
+    CALL 'hasNext(): Boolean' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
+CONTENT
+      1 GET_VAR 'result: Int' type=kotlin.Int origin=null
+      2 RETURN type=kotlin.Nothing from='factorial(Int): Int'
+OUTGOING -> NONE
+    Function exit: FUN public fun factorial(i: kotlin.Int): kotlin.Int
+
+// END FUN: factorial
+
+// END FILE: /factorial.kt
+