replacements: fix submit button not working in Chrome.

Fix the submit button in the post replacement dialog doing nothing in Chrome.

When the submit button in a dialog box is clicked, we tried to fire a 'submit' event on
the form to submit it. Apparently this no longer works in Chrome. `requestSubmit` is the
modern way to programmatically submit a form, but it's not supported by Safari, or by
versions of Firefox or Chrome released before 2019-2020.

https://developer.mozilla.org/en-US/docs/Web/API/HTMLFormElement/requestSubmit
https://caniuse.com/mdn-api_htmlformelement_requestsubmit

app/javascript/src/javascripts/utility.js

@@ -61,7 +61,13 @@ Utility.dialog = function(title, html) {
     buttons: {
       "Submit": function() {
         let form = $dialog.find("form").get(0);
-        Rails.fire(form, "submit");
+
+        if (form.requestSubmit) {
+          form.requestSubmit();
+        } else {
+          form.submit();
+          Rails.fire(form, "submit");
+        }
       },
       "Cancel": function() {
         $dialog.dialog("close");