Don't provide the enableXfa parameter to the BaseViewer constructor, and avoid the fallback bar with enableXfa = true set (PR 13069 follow-up)

Given that the `enableXfa` parameter must to be passed to the API/Worker, and thus included in the `getDocument` call, it's not necessary to include it when initializing the `PDFViewer`-instance used in the default viewer. (Also, in `AppOptions`, the parameter is clearly marked with `OptionKind.API`.)

Furthermore, we probably don't want to display the fallback bar (in Firefox) for XFA documents when `enableXfa = true` is set.

Author: Snuffleupagus

web/app.js

@@ -518,7 +518,6 @@ const PDFViewerApplication = {
       useOnlyCssZoom: AppOptions.get("useOnlyCssZoom"),
       maxCanvasPixels: AppOptions.get("maxCanvasPixels"),
       enableScripting: AppOptions.get("enableScripting"),
-      enableXfa: AppOptions.get("enableXfa"),
     });
     pdfRenderingQueue.setViewer(this.pdfViewer);
     pdfLinkService.setViewer(this.pdfViewer);
@@ -1561,7 +1560,11 @@ const PDFViewerApplication = {
       this.setTitle(contentDispositionFilename);
     }
 
-    if (info.IsXFAPresent && !info.IsAcroFormPresent) {
+    if (
+      info.IsXFAPresent &&
+      !info.IsAcroFormPresent &&
+      pdfDocument.isPureXfa // Implies that `enableXfa = true` was set.
+    ) {
       console.warn("Warning: XFA is not supported");
       this._delayedFallback(UNSUPPORTED_FEATURES.forms);
     } else if (