Add a unit-test to ensure that NullL10n won't diverge from the L10n-class

To prevent the *standalone* viewer-components from breaking, we need to ensure that the `NullL10n`-interface won't accidentally diverge from the actual `L10n`-implementations.

test/unit/pdf_viewer.component_spec.js

@@ -30,6 +30,7 @@ import { AnnotationLayerBuilder } from "../../web/annotation_layer_builder.js";
 import { DownloadManager } from "../../web/download_manager.js";
 import { EventBus } from "../../web/event_utils.js";
 import { GenericL10n } from "../../web/genericl10n.js";
+import { L10n } from "../../web/l10n.js";
 import { NullL10n } from "../../web/l10n_utils.js";
 import { PDFHistory } from "../../web/pdf_history.js";
 import { PDFPageView } from "../../web/pdf_page_view.js";
@@ -72,4 +73,14 @@ describe("pdfviewer_api", function () {
       XfaLayerBuilder,
     });
   });
+
+  it("checks that `NullL10n` implements all methods", function () {
+    const methods = Object.getOwnPropertyNames(NullL10n).sort();
+
+    const baseMethods = Object.getOwnPropertyNames(L10n.prototype)
+      .filter(m => m !== "constructor" && !m.startsWith("_"))
+      .sort();
+
+    expect(methods).toEqual(baseMethods);
+  });
 });

web/genericl10n.js

@@ -25,7 +25,7 @@ import { L10n } from "./l10n.js";
 class GenericL10n extends L10n {
   constructor(lang) {
     super({ lang });
-    this.setL10n(
+    this._setL10n(
       new DOMLocalization(
         [],
         GenericL10n.#generateBundles.bind(

web/l10n.js

@@ -31,7 +31,7 @@ class L10n {
     this.#dir = isRTL ?? L10n.#isRTL(this.#lang) ? "rtl" : "ltr";
   }
 
-  setL10n(l10n) {
+  _setL10n(l10n) {
     this.#l10n = l10n;
     if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("TESTING")) {
       document.l10n = l10n;