so rename it to that and add a OpenThenSwitchToDeck that actually
does that, using the Toggle varient as the callback from the
sidebar button which toggles the current deck on/off

which retains the features of

// tdf#67627 Clicking a second time on a Deck icon will close the Deck
// tdf#88241 Summoning an undocked sidebar a second time should close sidebar

but means that calls to OpenThenSwitchToDeck from e.g. slide layout
don't auto close it if that deck is already open

Change-Id: I3e3724626b93447a7ab6bc7032e9c6839dabcf55