KT-12877: modify tests to check whether mutable top-level properties of JsModule files are supported

js/js.translator/testData/box/multiModuleWrappers/amd/jsModuleOnPackage.kt

@@ -18,6 +18,7 @@ package foo
 
 @native val bar: Int = noImpl
 
+@native var mbar: Int = noImpl
 
 // MODULE: main(lib)
 // FILE: main.kt
@@ -35,5 +36,8 @@ fun box(): String {
     assertEquals(365, foo(42))
     assertEquals(423, bar)
 
+    mbar = 523
+    assertEquals(523, mbar)
+
     return "OK"
 }