make submission header buttons native

app/javascript/elements/download_button.js

@@ -21,6 +21,10 @@ export default targetable(class extends HTMLElement {
   downloadFiles () {
     if (!this.dataset.src) return
 
+    const download = window.webkit?.messageHandlers?.download
+
+    if (download) return download.postMessage({ src: this.dataset.src })
+
     this.toggleState()
 
     fetch(this.dataset.src).then(async (response) => {