JS: added js() diagnostics tests

idea/testData/diagnosticMessage/js/jsCodeErrorText.kt

@@ -0,0 +1,19 @@
+// !DIAGNOSTICS_NUMBER: 4
+// !DIAGNOSTICS: JSCODE_ERROR
+// !MESSAGE_TYPE: TEXT
+
+fun box() {
+    val i = "i"
+    val n = 10
+
+    js("var      = $n;")
+
+    js("""var a = 10;
+    var      = $n;
+    var c = 15;""")
+
+    js("""for (var $i =
+    )""")
+
+    js("var      = 10;")
+}