[api-minor] Add a new getXfaPageViewport helper function to support printing

This patch provides an overall simpler *and* more consistent way of handling the `viewport` parameter during printing of XFA forms, since it's now again guaranteed to always be an instance of `PageViewport`.
Furthermore, for anyone attempting to e.g. implement custom printing of XFA forms this probably cannot hurt either.

web/print_utils.js

@@ -15,26 +15,26 @@
 
 import { CSS_UNITS } from "./ui_utils.js";
 import { DefaultXfaLayerFactory } from "./xfa_layer_builder.js";
+import { getXfaPageViewport } from "pdfjs-lib";
 
 function getXfaHtmlForPrinting(printContainer, pdfDocument) {
   const xfaHtml = pdfDocument.allXfaHtml;
   const factory = new DefaultXfaLayerFactory();
   const scale = Math.round(CSS_UNITS * 100) / 100;
+
   for (const xfaPage of xfaHtml.children) {
     const page = document.createElement("div");
     page.className = "xfaPrintedPage";
     printContainer.appendChild(page);
 
-    const { width, height } = xfaPage.attributes.style;
-    const viewBox = [0, 0, parseInt(width), parseInt(height)];
-    const viewport = { viewBox, scale, rotation: 0 };
-
     const builder = factory.createXfaLayerBuilder(
       /* pageDiv = */ page,
       /* pdfPage = */ null,
       /* annotationStorage = */ pdfDocument.annotationStorage,
       /* xfaHtml = */ xfaPage
     );
+    const viewport = getXfaPageViewport(xfaPage, { scale });
+
     builder.render(viewport, "print");
   }
 }

web/xfa_layer_builder.js

@@ -44,9 +44,8 @@ class XfaLayerBuilder {
    */
   render(viewport, intent = "display") {
     if (intent === "print") {
-      viewport.dontFlip = true;
       const parameters = {
-        viewport,
+        viewport: viewport.clone({ dontFlip: true }),
         div: this.div,
         xfa: this.xfaHtml,
         page: null,
@@ -76,6 +75,7 @@ class XfaLayerBuilder {
           xfa,
           page: this.pdfPage,
           annotationStorage: this.annotationStorage,
+          intent,
         };
 
         if (this.div) {