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

js/js.translator/testData/box/classObject/inTrait.kt

@@ -0,0 +1,11 @@
+package foo
+
+interface A {
+    companion object {
+        val OK: String = "OK"
+    }
+}
+
+fun box(): String {
+    return A.OK
+}