migrate pdf_viewer to dynamic import

app/assets/javascripts/blob/pdf_viewer.js

 import renderPDF from './pdf';
 
-document.addEventListener('DOMContentLoaded', renderPDF);
+export default renderPDF;

app/assets/javascripts/blob/viewer/index.js

@@ -35,6 +35,9 @@ export default class BlobViewer {
       case 'notebook':
         initViewer(import(/* webpackChunkName: 'notebook_viewer' */ '../notebook_viewer'));
         break;
+      case 'pdf':
+        initViewer(import(/* webpackChunkName: 'pdf_viewer' */ '../pdf_viewer'));
+        break;
       default:
         break;
     }

app/views/projects/blob/viewers/_pdf.html.haml

-- content_for :page_specific_javascripts do
-  = webpack_bundle_tag('common_vue')
-  = webpack_bundle_tag('pdf_viewer')
-
 .file-content#js-pdf-viewer{ data: { endpoint: blob_raw_path } }

config/webpack.config.js

@@ -50,7 +50,6 @@ function generateEntries() {
   const manualEntries = {
     monitoring:           './monitoring/monitoring_bundle.js',
     mr_notes:             './mr_notes/index.js',
-    pdf_viewer:           './blob/pdf_viewer.js',
     protected_branches:   './protected_branches',
     registry_list:        './registry/index.js',
     sketch_viewer:        './blob/sketch_viewer.js',
@@ -248,7 +247,6 @@ const config = {
         'groups',
         'monitoring',
         'mr_notes',
-        'pdf_viewer',
         'pipelines',
         'pipelines_details',
         'registry_list',