Re-factor how the GenericL10n class fetches localization-data

- Re-factor the existing `fetchData` helper function such that it can fetch more types of data, and it now supports "arraybuffer", "json", and "text".
   This only needed minor adjustments in the `DOMCMapReaderFactory` and `DOMStandardFontDataFactory` classes.[1]

 - Expose the `fetchData` helper function in the API, such that the viewer is able to access it.

 - Use the `fetchData` helper function in the `GenericL10n` class, since this should allow fetching of localization-data even if the default viewer is run in an environment without support for the Fetch API.

---
[1] While testing this I also noticed a minor inconsistency when handling standard font-data on the worker-thread.

web/genericl10n.js

@@ -17,6 +17,7 @@
 
 import { FluentBundle, FluentResource } from "fluent-bundle";
 import { DOMLocalization } from "fluent-dom";
+import { fetchData } from "pdfjs-lib";
 import { L10n } from "./l10n.js";
 
 /**
@@ -71,8 +72,8 @@ class GenericL10n extends L10n {
       return null;
     }
     const url = new URL(path, baseURL);
-    const data = await fetch(url);
-    const text = await data.text();
+    const text = await fetchData(url, /* type = */ "text");
+
     const resource = new FluentResource(text);
     const bundle = new FluentBundle(lang);
     const errors = bundle.addResource(resource);
@@ -84,8 +85,8 @@ class GenericL10n extends L10n {
 
   static async #getPaths() {
     const { href } = document.querySelector(`link[type="application/l10n"]`);
-    const data = await fetch(href);
-    const paths = await data.json();
+    const paths = await fetchData(href, /* type = */ "json");
+
     return { baseURL: href.replace(/[^/]*$/, "") || "./", paths };
   }
 }

web/pdfjs.js

@@ -35,6 +35,7 @@ const {
   createValidAbsoluteUrl,
   DOMSVGFactory,
   FeatureTest,
+  fetchData,
   getDocument,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,
@@ -80,6 +81,7 @@ export {
   createValidAbsoluteUrl,
   DOMSVGFactory,
   FeatureTest,
+  fetchData,
   getDocument,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,