[K/JS] Add support of compilation with ES-classes

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

@@ -0,0 +1,24 @@
+@JsName("Set")
+external class JsSet<T> {
+    fun has(value: T): Boolean
+}
+
+external open class JsFoo(value: String) {
+    val value: String
+    companion object {
+        val instances: JsSet<JsFoo>
+    }
+}
+
+class KotlinFoo(value: String) : JsFoo(value) {
+    fun existsInJs(): Boolean = JsFoo.instances.has(this)
+}
+
+fun box(): String {
+    val foo = KotlinFoo("TEST")
+
+    assertEquals("TEST", foo.value)
+    assertEquals(true, foo.existsInJs())
+
+    return "OK"
+}