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

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

@@ -0,0 +1,20 @@
+package foo
+
+interface Base {
+    abstract fun foo(x: String): String
+}
+
+class BaseImpl(val s: String) : Base {
+    override fun foo(x: String): String = "Base: ${s}:${x}"
+}
+
+fun newBase(s: String): Base = BaseImpl(s)
+
+class Derived() : Base by newBase("test")
+
+
+fun box(): String {
+    assertEquals("Base: test:!!", Derived().foo("!!"), "delegation by function expression")
+
+    return "OK"
+}