XFA - Add <a> element in button when an url is detected (bug 1716758)

- it aims to fix https://bugzilla.mozilla.org/show_bug.cgi?id=1716758;
  - some buttons have a JS action with the pattern `app.launchURL(...)` (or similar) so extract when it's possible the url and generate a <a> element with the href equals to the found url;
  - pdf.js already had some code to handle that so this patch slightly refactor that.

src/core/xfa/html_utils.js

@@ -26,10 +26,14 @@ import {
   $toStyle,
   XFAObject,
 } from "./xfa_object.js";
+import {
+  addDefaultProtocolToUrl,
+  tryConvertUrlEncoding,
+} from "../core_utils.js";
+import { createValidAbsoluteUrl, warn } from "../../shared/util.js";
 import { getMeasurement, stripQuotes } from "./utils.js";
 import { selectFont } from "./fonts.js";
 import { TextMeasure } from "./text.js";
-import { warn } from "../../shared/util.js";
 
 function measureToString(m) {
   if (typeof m === "string") {
@@ -633,11 +637,24 @@ function setFontFamily(xfaFont, node, fontFinder, style) {
   }
 }
 
+function fixURL(str) {
+  if (typeof str === "string") {
+    let url = addDefaultProtocolToUrl(str);
+    url = tryConvertUrlEncoding(url);
+    const absoluteUrl = createValidAbsoluteUrl(url);
+    if (absoluteUrl) {
+      return absoluteUrl.href;
+    }
+  }
+  return null;
+}
+
 export {
   computeBbox,
   createWrapper,
   fixDimensions,
   fixTextIndent,
+  fixURL,
   isPrintOnly,
   layoutClass,
   layoutNode,