Move the sidebar toggleButton event listener into PDFSidebar

This is consistent with other functionality, such as e.g. `SecondaryToolbar` and `PDFFindBar`.

web/app.js

@@ -1654,10 +1654,6 @@ function webViewerInitialized() {
     }
   }, true);
 
-  appConfig.sidebar.toggleButton.addEventListener('click', function() {
-    PDFViewerApplication.pdfSidebar.toggle();
-  });
-
   try {
     webViewerOpenFileViaURL(file);
   } catch (reason) {

web/pdf_sidebar.js

@@ -390,6 +390,10 @@ class PDFSidebar {
       }
     });
 
+    this.toggleButton.addEventListener('click', () => {
+      this.toggle();
+    });
+
     // Buttons for switching views.
     this.thumbnailButton.addEventListener('click', () => {
       this.switchView(SidebarView.THUMBS);