Enable the import/no-cycle ESLint plugin rule

Having cyclical imports is obviously not a good idea, and this ESLint plugin rule can help detect those; please see https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/no-cycle.md

src/scripting_api/app.js

@@ -13,18 +13,19 @@
  * limitations under the License.
  */
 
+import {
+  FORMS_VERSION,
+  USERACTIVATION_CALLBACKID,
+  VIEWER_TYPE,
+  VIEWER_VARIATION,
+  VIEWER_VERSION,
+} from "./app_utils.js";
 import { Color } from "./color.js";
 import { EventDispatcher } from "./event.js";
 import { FullScreen } from "./fullscreen.js";
 import { PDFObject } from "./pdf_object.js";
 import { Thermometer } from "./thermometer.js";
 
-const VIEWER_TYPE = "PDF.js";
-const VIEWER_VARIATION = "Full";
-const VIEWER_VERSION = 21.00720099;
-const FORMS_VERSION = 21.00720099;
-const USERACTIVATION_CALLBACKID = 0;
-
 class App extends PDFObject {
   constructor(data) {
     super(data);
@@ -654,4 +655,4 @@ class App extends PDFObject {
   }
 }
 
-export { App, USERACTIVATION_CALLBACKID };
+export { App };

src/scripting_api/app_utils.js

@@ -0,0 +1,31 @@
+/* Copyright 2020 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+const VIEWER_TYPE = "PDF.js";
+const VIEWER_VARIATION = "Full";
+const VIEWER_VERSION = 21.00720099;
+const FORMS_VERSION = 21.00720099;
+
+const USERACTIVATION_CALLBACKID = 0;
+const USERACTIVATION_MAXTIME_VALIDITY = 5000;
+
+export {
+  FORMS_VERSION,
+  USERACTIVATION_CALLBACKID,
+  USERACTIVATION_MAXTIME_VALIDITY,
+  VIEWER_TYPE,
+  VIEWER_VARIATION,
+  VIEWER_VERSION,
+};

src/scripting_api/event.js

@@ -13,9 +13,10 @@
  * limitations under the License.
  */
 
-import { USERACTIVATION_CALLBACKID } from "./app.js";
-
-const USERACTIVATION_MAXTIME_VALIDITY = 5000;
+import {
+  USERACTIVATION_CALLBACKID,
+  USERACTIVATION_MAXTIME_VALIDITY,
+} from "./app_utils.js";
 
 class Event {
   constructor(data) {