Re-factor PDFPrintServiceFactory to use import maps

This is very old code, which can (ever so slightly) be simplified now that import maps are available.

web/interfaces.js

@@ -217,4 +217,23 @@ class IL10n {
   resume() {}
 }
 
-export { IDownloadManager, IL10n, IPDFLinkService, IRenderableView };
+/**
+ * @interface
+ */
+class IPDFPrintServiceFactory {
+  static get supportsPrinting() {
+    return false;
+  }
+
+  static createPrintService() {
+    throw new Error("Not implemented: createPrintService");
+  }
+}
+
+export {
+  IDownloadManager,
+  IL10n,
+  IPDFLinkService,
+  IPDFPrintServiceFactory,
+  IRenderableView,
+};