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

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

@@ -0,0 +1,16 @@
+package foo
+
+import kotlin.reflect.KProperty
+
+class Delegate {
+}
+
+operator fun Delegate.getValue(t: Any?, p: KProperty<*>): Int = 1
+
+class A {
+    val prop: Int by Delegate()
+}
+
+fun box(): String {
+    return if (A().prop == 1) "OK" else "fail"
+}