Fix JS source maps for delegates and backing fields

js/js.translator/testData/lineNumbers/delegatedProperty.kt

@@ -0,0 +1,18 @@
+import kotlin.reflect.*
+
+open class A {
+    var x: String by
+            B()
+}
+
+class B {
+    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
+        return "OK"
+    }
+
+    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
+        println(value)
+    }
+}
+
+// LINES: 4 5 4 4 2 * 10 * 14