[api-minor] Move to Fluent for the localization (bug 1858715)

- For the generic viewer we use @fluent/dom and @fluent/bundle
- For the builtin pdf viewer in Firefox, we set a localization url
  and then we rely on document.l10n which is a DOMLocalization object.

web/password_prompt.js

@@ -85,7 +85,7 @@ class PasswordPrompt {
       this.input.focus();
     }
     this.label.textContent = await this.l10n.get(
-      `password_${passwordIncorrect ? "invalid" : "label"}`
+      `pdfjs-password-${passwordIncorrect ? "invalid" : "label"}`
     );
   }