[IMP] web: open external links of PDFs in new tab

Reimplementation of 74fa91e0b3 on top of
new version of pdfjs. See previous commit for explanation.

Ideally we would set that behaviour from the outside using
e.g. `PDFViewerApplicationOptions.set` but there are multiple
locations from which we embed the viewer, which makes that a difficult
proposition. There should probably be a clean component which handles
loading the library, configuring it to our specifications (possibly on
a per-embed basis), and exposing both manipulations methods and events
which pdfjs triggers on its eventBus.

Part-of: odoo/odoo#100067

addons/web/static/lib/pdfjs/web/viewer.js

@@ -16861,7 +16861,7 @@ class BasePreferences {
         "enablePermissions": false,
         "enablePrintAutoRotate": true,
         "enableScripting": true,
-        "externalLinkTarget": 0,
+        "externalLinkTarget": 2,
         "historyUpdateUrl": false,
         "ignoreDestinationZoom": false,
         "forcePageColors": false,