[api-minor] Add partial support for the "GoToE" action (issue 8844)

*Please note:* The referenced issue is the only mention that I can find, in either GitHub or Bugzilla, of "GoToE" actions.
Hence why I've purposely settled for a very simple, and partial, "GoToE" implementation to avoid complicating things initially.[1] In particular, this patch only supports "GoToE" actions that references the /EmbeddedFiles-dict in the PDF document.

See https://web.archive.org/web/20220309040754if_/https://www.adobe.com/content/dam/acom/en/devnet/pdf/pdfs/PDF32000_2008.pdf#G11.2048909

---
[1] Usually I always prefer having *real-world* test-cases to work with, whenever I'm implementing new features.

web/app.js

@@ -636,6 +636,7 @@ const PDFViewerApplication = {
       container: appConfig.sidebar.outlineView,
       eventBus,
       linkService: pdfLinkService,
+      downloadManager,
     });
 
     this.pdfAttachmentViewer = new PDFAttachmentViewer({

web/pdf_outline_viewer.js

@@ -20,8 +20,9 @@ import { SidebarView } from "./ui_utils.js";
 /**
  * @typedef {Object} PDFOutlineViewerOptions
  * @property {HTMLDivElement} container - The viewer element.
- * @property {IPDFLinkService} linkService - The navigation/linking service.
  * @property {EventBus} eventBus - The application event bus.
+ * @property {IPDFLinkService} linkService - The navigation/linking service.
+ * @property {DownloadManager} downloadManager - The download manager.
  */
 
 /**
@@ -37,6 +38,7 @@ class PDFOutlineViewer extends BaseTreeViewer {
   constructor(options) {
     super(options);
     this.linkService = options.linkService;
+    this.downloadManager = options.downloadManager;
 
     this.eventBus._on("toggleoutlinetree", this._toggleAllTreeItems.bind(this));
     this.eventBus._on(
@@ -109,7 +111,10 @@ class PDFOutlineViewer extends BaseTreeViewer {
   /**
    * @private
    */
-  _bindLink(element, { url, newWindow, action, dest, setOCGState }) {
+  _bindLink(
+    element,
+    { url, newWindow, action, attachment, dest, setOCGState }
+  ) {
     const { linkService } = this;
 
     if (url) {
@@ -124,6 +129,18 @@ class PDFOutlineViewer extends BaseTreeViewer {
       };
       return;
     }
+    if (attachment) {
+      element.href = linkService.getAnchorUrl("");
+      element.onclick = () => {
+        this.downloadManager.openOrDownloadData(
+          element,
+          attachment.content,
+          attachment.filename
+        );
+        return false;
+      };
+      return;
+    }
     if (setOCGState) {
       element.href = linkService.getAnchorUrl("");
       element.onclick = () => {