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

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

@@ -1,6 +1,6 @@
 package foo
 
-fun box(): Boolean {
+fun box(): String {
     val t = myRun {
         object {
             fun boo(param: String): String {
@@ -9,5 +9,5 @@ fun box(): Boolean {
         }
     }
 
-    return t.boo("OK") == "OK"
+    return t.boo("OK")
 }

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

@@ -28,8 +28,11 @@ fun foo(f: () -> Unit) {
     f()
 }
 
-fun box(): Boolean {
+fun box(): String {
     val a = A()
     a.f()
-    return a.i == 6 && a.bar() == 32
+    if (a.i != 6) return "fail1: ${a.i}"
+    if (a.bar() != 32) return "fail2: ${a.bar()}"
+
+    return "OK"
 }