Refactor all .length === 0 patterns in JS (#30045)

This pattern comes of often during review, so let's fix it once and for
all. Did not test, but changes are trivial enough imho.

web_src/js/features/common-global.js

@@ -19,7 +19,7 @@ const {appUrl, appSubUrl, csrfToken, i18n} = window.config;
 export function initGlobalFormDirtyLeaveConfirm() {
   // Warn users that try to leave a page after entering data into a form.
   // Except on sign-in pages, and for forms marked as 'ignore-dirty'.
-  if ($('.user.signin').length === 0) {
+  if (!$('.user.signin').length) {
     $('form:not(.ignore-dirty)').areYouSure();
   }
 }