KT-2752: add basic tests for JsName

js/js.translator/testData/box/jsName/privateMethod.kt

@@ -0,0 +1,15 @@
+package foo
+
+object A {
+    @JsName("js_f") private fun f(x: Int) = "f($x)"
+}
+
+fun test() = js("""
+return Kotlin.modules.JS_TESTS.foo.A.js_f(23);
+""")
+
+fun box(): String {
+    val result = test()
+    assertEquals("f(23)", result);
+    return "OK"
+}