docs: adds Native-UI Open external links and the file manager Fiddle example (#20524)

docs/fiddles/native-ui/external-links-file-manager/renderer.js

@@ -0,0 +1,13 @@
+const { shell } = require('electron')
+const os = require('os')
+
+const exLinksBtn = document.getElementById('open-ex-links')
+const fileManagerBtn = document.getElementById('open-file-manager')
+
+fileManagerBtn.addEventListener('click', (event) => {
+  shell.showItemInFolder(os.homedir())
+})
+
+exLinksBtn.addEventListener('click', (event) => {
+  shell.openExternal('http://electron.atom.io')
+})