draft: app: don't expand file dialog

Fix #10612 (closed) by disabling top level resize.

Looks like I finally managed to fix one of my bite-size bugs before Alx Sa 😉

Edit: Marking as draft as I'm not certain of the best solution. This MR is fine if 2.10.x behavior is "good enough".

Otherwise file dialogs with persistent state of file type expanders would probably be the most elegant solution.