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

js/js.translator/testData/box/delegateProperty/setAsExtensionFun.kt

@@ -0,0 +1,24 @@
+package foo
+
+import kotlin.reflect.KProperty
+
+class Delegate {
+    var inner = 1
+    operator fun getValue(t: Any?, p: KProperty<*>): Int = inner
+}
+
+operator fun Delegate.setValue(t: Any?, p: KProperty<*>, i: Int) {
+    inner = i
+}
+
+class A {
+    var prop: Int by Delegate()
+}
+
+fun box(): String {
+    val c = A()
+    if (c.prop != 1) return "fail get"
+    c.prop = 2
+    if (c.prop != 2) return "fail set"
+    return "OK"
+}