[IMP] design: add an icon behind external links

The external links' target attribute is now also updated to open the
link in a new tab. In addition, the "[source]" link of autodoc's models
is moved right next to the name of the model to correctly position the
icon.

task-2790244

closes odoo/documentation#2167

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>
Co-authored-by: Antoine Vandevenne (anv) <anv@odoo.com>

extensions/odoo_theme/static/js/layout.js

@@ -3,10 +3,15 @@
     document.addEventListener('DOMContentLoaded', function () {
         const content = document.getElementById('o_content');
 
-        // Enforce the presence of the `img-fluid` class on all images in the body
+        // Enforce the presence of the `img-fluid` class on all images in the body.
         content.querySelectorAll('img').forEach(image => {
             image.classList.add('img-fluid');
         });
+
+        // Make all external links open in a new tab by default.
+        content.querySelectorAll('a.external').forEach(externalLink => {
+            externalLink.setAttribute('target', '_blank');
+        })
     });
 
 })();