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

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

@@ -0,0 +1,27 @@
+package foo
+
+interface Base {
+    abstract fun foo(x: String): String
+    var prop: String
+}
+
+class BaseImpl(val s: String) : Base {
+    override fun foo(x: String): String = "Base: ${s}:${x}"
+    override var prop: String = "prop"
+}
+
+class Derived(b: Base) : Base by b
+
+
+fun box(): String {
+    var d = Derived(BaseImpl("test"))
+    assertEquals("Base: test:!!", d.foo("!!"), "delegation by argument, function member")
+    assertEquals("prop", d.prop, "delegation by argument, get property")
+
+    d.prop = "new value"
+    assertEquals("new value", d.prop, "delegation by argument, set property")
+
+    return "OK"
+}
+
+