apps: Improve a11y of the remove buttons from handler_dialog
requested to merge automerisnaranja/gnome-control-center:tooltip-remove-button-handler-dialog into main
In the File & Link Associations dialog (handler_dialog), the remove button from list rows doesn't have a tooltip; also, Orca doesn't read this button properly, since there is no a11y label.
Fix that by adding a tooltip, which also acts as an a11y label.
