Slightly re-factor how we pre-load fonts and images in XFA documents

Rather than "manually" invoking the methods from the `src/core/worker.js` file we introduce a single `PDFDocument`-method that handles this for us, and make the current methods private.
Since this code is only invoked at most *once* per document, and only for XFA documents, we can use `BasePdfManager.prototype.ensureDoc` directly rather than needing a stand-alone method.

Author: Snuffleupagus

src/core/document.js

@@ -1237,15 +1237,15 @@ class PDFDocument {
     return this.xfaFactory ? this.xfaFactory.getPages() : null;
   }
 
-  async loadXfaImages() {
+  async #loadXfaImages() {
     const xfaImages = await this.pdfManager.ensureCatalog("xfaImages");
     if (!xfaImages) {
       return;
     }
     this.xfaFactory.setImages(xfaImages);
   }
 
-  async loadXfaFonts(handler, task) {
+  async #loadXfaFonts(handler, task) {
     const acroForm = await this.pdfManager.ensureCatalog("acroForm");
     if (!acroForm) {
       return;
@@ -1264,18 +1264,19 @@ class PDFDocument {
 
     const options = Object.assign(
       Object.create(null),
-      this.pdfManager.evaluatorOptions
+      this.pdfManager.evaluatorOptions,
+      { useSystemFonts: false }
     );
-    options.useSystemFonts = false;
+    const { builtInCMapCache, fontCache, standardFontDataCache } = this.catalog;
 
     const partialEvaluator = new PartialEvaluator({
       xref: this.xref,
       handler,
       pageIndex: -1,
       idFactory: this._globalIdFactory,
-      fontCache: this.catalog.fontCache,
-      builtInCMapCache: this.catalog.builtInCMapCache,
-      standardFontDataCache: this.catalog.standardFontDataCache,
+      fontCache,
+      builtInCMapCache,
+      standardFontDataCache,
       options,
     });
     const operatorList = new OperatorList();
@@ -1383,6 +1384,15 @@ class PDFDocument {
     this.xfaFactory.appendFonts(pdfFonts, reallyMissingFonts);
   }
 
+  loadXfaResources(handler, task) {
+    return Promise.all([
+      this.#loadXfaFonts(handler, task).catch(() => {
+        // Ignore errors, to allow the document to load.
+      }),
+      this.#loadXfaImages(),
+    ]);
+  }
+
   serializeXfaData(annotationStorage) {
     return this.xfaFactory
       ? this.xfaFactory.serializeData(annotationStorage)

src/core/pdf_manager.js

@@ -115,14 +115,6 @@ class BasePdfManager {
     return this.pdfDocument.fontFallback(id, handler);
   }
 
-  loadXfaFonts(handler, task) {
-    return this.pdfDocument.loadXfaFonts(handler, task);
-  }
-
-  loadXfaImages() {
-    return this.pdfDocument.loadXfaImages();
-  }
-
   cleanup(manuallyTriggered = false) {
     return this.pdfDocument.cleanup(manuallyTriggered);
   }

src/core/worker.js

@@ -170,18 +170,11 @@ class WorkerMessageHandler {
 
       const isPureXfa = await pdfManager.ensureDoc("isPureXfa");
       if (isPureXfa) {
-        const task = new WorkerTask("loadXfaFonts");
+        const task = new WorkerTask("loadXfaResources");
         startWorkerTask(task);
 
-        await Promise.all([
-          pdfManager
-            .loadXfaFonts(handler, task)
-            .catch(reason => {
-              // Ignore errors, to allow the document to load.
-            })
-            .then(() => finishWorkerTask(task)),
-          pdfManager.loadXfaImages(),
-        ]);
+        await pdfManager.ensureDoc("loadXfaResources", [handler, task]);
+        finishWorkerTask(task);
       }
 
       const [numPages, fingerprints] = await Promise.all([