Use ESLint to ensure that exports are sorted alphabetically

There's built-in ESLint rule, see `sort-imports`, to ensure that all `import`-statements are sorted alphabetically, since that often helps with readability.
Unfortunately there's no corresponding rule to sort `export`-statements alphabetically, however there's an ESLint plugin which does this; please see https://www.npmjs.com/package/eslint-plugin-sort-exports

The only downside here is that it's not automatically fixable, but the re-ordering is a one-time "cost" and the plugin will help maintain a *consistent* ordering of `export`-statements in the future.
*Note:* To reduce the possibility of introducing any errors here, the re-ordering was done by simply selecting the relevant lines and then using the built-in sort-functionality of my editor.

web/pdf_viewer.component.js

@@ -37,20 +37,20 @@ const pdfjsVersion = PDFJSDev.eval("BUNDLE_VERSION");
 const pdfjsBuild = PDFJSDev.eval("BUNDLE_BUILD");
 
 export {
-  PDFViewer,
-  PDFSinglePageViewer,
-  PDFPageView,
-  PDFLinkService,
-  SimpleLinkService,
-  TextLayerBuilder,
-  DefaultTextLayerFactory,
   AnnotationLayerBuilder,
   DefaultAnnotationLayerFactory,
-  PDFHistory,
-  PDFFindController,
-  EventBus,
+  DefaultTextLayerFactory,
   DownloadManager,
-  ProgressBar,
+  EventBus,
   GenericL10n,
   NullL10n,
+  PDFFindController,
+  PDFHistory,
+  PDFLinkService,
+  PDFPageView,
+  PDFSinglePageViewer,
+  PDFViewer,
+  ProgressBar,
+  SimpleLinkService,
+  TextLayerBuilder,
 };