XFA - Add a layer to display XFA forms (#13069)

- add an option to enable XFA rendering if any;
  - for now, let the canvas layer: it could be useful to implement XFAF forms (embedded pdf in xml stream for the background and xfa form for the foreground);
  - ui elements in template DOM are pretty close to their html counterpart so we generate a fake html DOM from template one:
    - it makes easier to translate template properties to html ones;
    - it makes faster the creation of the html element in the main thread.

web/interfaces.js

@@ -204,6 +204,18 @@ class IPDFAnnotationLayerFactory {
   ) {}
 }
 
+/**
+ * @interface
+ */
+class IPDFXfaLayerFactory {
+  /**
+   * @param {HTMLDivElement} pageDiv
+   * @param {PDFPage} pdfPage
+   * @returns {XfaLayerBuilder}
+   */
+  createXfaLayerBuilder(pageDiv, pdfPage) {}
+}
+
 /**
  * @interface
  */
@@ -243,5 +255,6 @@ export {
   IPDFHistory,
   IPDFLinkService,
   IPDFTextLayerFactory,
+  IPDFXfaLayerFactory,
   IRenderableView,
 };