Browsing Chuvash translation

Create a GtkFileChooserDialog, not a GtkFileChooserNative, because
* with GtkFileChooserNative the GFile that we obtain (in flatpak)
* doesn't have the real path to the file, so it would ruin some
* features for text editors:
* - showing the directory in parentheses in the window title, or in the
*   tab tooltip;
* - opening a recent file.
* Basically everywhere where the directory is shown.