Image export options

I'd like to have a UI to modify additional options of an image format when exporting a render. These should be saved globally for each format (will be restored after switching to a different format).
To modify these options, a button is added alongside the format dropdown. When a format has options, it will open a dialog box or expand a collapsed field, otherwise it will be disabled.

Start by locating the export UI, format dropdown, and image-format handling described in the issue. Trace how the selected format is stored and restored, then identify how format-specific options can be represented. Done means the options control appears beside the dropdown, opens or expands when supported, remains disabled otherwise, and persists globally per format.

Written by the indexing model from the issue text.