XFA - Save filled data in the pdf when downloading the file (Bug 1716288)

- when binding (after parsing) we get a map between some template nodes and some data nodes;
  - so set user data in input handlers in using data node uids in the annotation storage;
  - to save the form, just put the value we have in the storage in the correct data nodes, serialize the xml as a string and then write the string at the end of the pdf using src/core/writer.js;
  - fix few bugs around data bindings:
    - the "Off" issue in Bug 1716980.

src/core/pdf_manager.js

@@ -77,6 +77,10 @@ class BasePdfManager {
     return this.pdfDocument.loadXfaFonts(handler, task);
   }
 
+  serializeXfaData(annotationStorage) {
+    return this.pdfDocument.serializeXfaData(annotationStorage);
+  }
+
   cleanup(manuallyTriggered = false) {
     return this.pdfDocument.cleanup(manuallyTriggered);
   }