KT-12733 'rangeTo' as a non-qualified call is not optimized in 'for'

Use ResolvedCall corresponding to 'for' loop range expression
for optimized "for-in-range-literal".
Cleanup.

compiler/testData/codegen/box/ranges/forNullableIntInRangeWithImplicitReceiver.kt

@@ -0,0 +1,20 @@
+// WITH_RUNTIME
+
+import kotlin.test.assertEquals
+
+fun suppressBoxingOptimization(ni: Int?) {}
+
+fun Int.digitsUpto(end: Int): Int {
+    var sum = 0
+    for (i: Int? in rangeTo(end)) {
+        suppressBoxingOptimization(i)
+        sum = sum*10 + i!!
+    }
+    return sum
+}
+
+fun box(): String {
+    assertEquals(1234, 1.digitsUpto(4))
+    return "OK"
+}
+