[JS BE] add tests for es6-classes

js/js.translator/testData/box/es6classes/fieldAccess.kt

@@ -0,0 +1,13 @@
+// EXPECTED_REACHABLE_NODES: 1340
+open class A(val x: Int)
+
+class B(val p: Int, val q: Int): A(p + q)
+
+fun box(): String {
+    val b = B(2, 3)
+    assertEquals(b.p, 2)
+    assertEquals(b.q, 3)
+    assertEquals(b.x, 5)
+
+    return "OK"
+}