add Request closing support to all rejectable dialogs

this ensures that the dialog goes away when the app disappears while the
dialog is still up (e.g. when ctrl-c'ing the app)

this simply refactors the existing Request code to correctly register on
the path and then emit the closerequest that gets routed to the ::reject
function of the dialog. for extra flexibility this is implemented as a
template such that the concrete type doesn't matter so long as it has a
reject slot.

BUG: 386385