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

js/js.translator/testData/box/closure/wrappedVariableInExtensionFun.kt

@@ -0,0 +1,10 @@
+package foo
+
+fun Any.foo(n: Int): () -> Boolean {
+    var count = n
+    return { --count >= 0 }
+}
+
+fun box(): String {
+    return if (1.foo(3)() && !1.foo(0)()) "OK" else "fail"
+}