feat(bar): hide when leaving komorebi's virtual desktop

This commit adds a new VirtualDesktopNotification which is used to
notify subscribers when the user leaves and enters the virtual desktop
associated with komorebi.

komorebi-bar consumes these notifications to minmize and restore the bar
appropriately depending on the currently focused virtual desktop.

re #1420

komorebi-client/src/lib.rs

@@ -70,6 +70,7 @@ pub use komorebi::State;
 pub use komorebi::StaticConfig;
 pub use komorebi::SubscribeOptions;
 pub use komorebi::TabsConfig;
+pub use komorebi::VirtualDesktopNotification;
 pub use komorebi::WindowContainerBehaviour;
 pub use komorebi::WindowsApi;
 pub use komorebi::WorkspaceConfig;