Rename *.jet -> *.kt in codegen tests

compiler/testData/codegen/objects/objectLiteral.kt

@@ -0,0 +1,17 @@
+class C(x: Int, val y : Int) {
+  fun initChild(var x: Int) : java.lang.Object {
+    return object : java.lang.Object() {
+      override fun toString(): String? {
+          x = x + y
+          return "child" + x
+      }
+    }
+  }
+
+  val child = initChild(x)
+}
+
+fun box(): String {
+  val c = C(10,3)
+  return if (c.child.toString() == "child13" && c.child.toString() == "child16" && c.child.toString() == "child19") "OK" else "fail"
+}