Allow screenreader users to easily access and use the AdvancedSearch UI.
[x] Allow general keyboard interaction ( see T181162 )
[ ] Set collapse / expand states to the expandable pane
[ ] Set `role=button` on expandable pane
[ ] Set fitting ARIA roles to interactive elements ( see  ) ---> Small investigation what is left over that should be done
 The file type dropdown cannot be navigated over the specific file types, just the categories (Audio/video etc) using VoiceOver are browsable. ---> Can Michi reproduce?
 The file type dropdown does not allow you to descend (ctrl-option-space) into the list with VoiceOver ---> Can Michi reproduce?
 "Search in" should be a lable for the namespace selection input box. <strong> should be replaced by <label> or maybe even a label widget
 File width and File height labels are not connected to any fields. It should lead you to at least the first drop down (e.g. "greater than"). If possible, "px" can also be added as a label to the field