Drop Throwable#printStackTrace, make it a JVM-specific extension

compiler/testData/codegen/box/objects/kt1136.kt

@@ -41,10 +41,10 @@ public class SomeClass() {
     }
 }
 
-public fun box():String {
+public fun box(): String {
     var obj = SomeClass()
-    return if(obj.status == null) "OK" else {
-        obj.status?.printStackTrace()
+    return if (obj.status == null) "OK" else {
+        (obj.status as java.lang.Throwable).printStackTrace()
         "failed"
     }
 }