Bug 1901308 - Show profile backup errors and keep modals open r=backup-reviewers,fluent-reviewers,firefox-desktop-core-reviewers ,mconley,bolsson

Currently, clicking "confirm" buttons on modals in the profile backup settings menu will always close the modals regardless of whether the operation succeeded or failed. In the case of errors, users don't know that something went wrong. It's better to keep the modals open and display an error so that the user knows what to do next and can try to fix the issue, if applicable.

Differential Revision: https://phabricator.services.mozilla.com/D218358

browser/components/backup/BackupService.sys.mjs

@@ -2753,6 +2753,7 @@ export class BackupService extends EventTarget {
       lazy.logConsole.error(
         `Failed to set parent directory ${parentDirPath}. ${e}`
       );
+      throw e;
     }
   }