JS: create new common directory for all generated tests, migrate several tests there

js/js.translator/testData/box/delegation/delegationChain.kt

@@ -0,0 +1,31 @@
+package foo
+
+interface Base {
+    abstract fun foo(x: String): String
+    var prop: String
+}
+
+class BaseImpl(val s: String) : Base {
+    override fun foo(x: String) = "BaseImpl.foo: ${s}:${x}"
+    override var prop: String = "init"
+        set(value) {
+            field = "prop:${value}"
+        }
+}
+
+class Base2Impl(val s: String) : Base by BaseImpl("${s} by BaseImpl")
+
+class Derived(val s: String) : Base by Base2Impl("${s} by Base2Impl")
+
+fun box(): String {
+    assertEquals("BaseImpl.foo: Derived by Base2Impl by BaseImpl:!!", Derived("Derived").foo("!!"))
+
+    var d = Derived("Derived")
+    assertEquals("init", d.prop)
+
+    d.prop = "A"
+    assertEquals("prop:A", d.prop)
+
+    return "OK"
+}
+