chore: add alt-tab navigation with update_mru flag and MRU-based taskbar rendering

include/client.h

@@ -18,7 +18,7 @@ void client_unmanage(Client *client);
 Client *client_find_by_window(Window window);
 Client *client_find_by_frame(Window frame);
 
-void client_focus(Client *client);
+void client_focus(Client *client, bool update_mru);
 void client_unfocus(Client *client);
 void client_raise(Client *client);
 void client_lower(Client *client);

include/dwn.h

@@ -171,6 +171,9 @@ typedef struct {
 
     Client *pending_focus_client;
     long pending_focus_time;
+
+    bool is_alt_tabbing;
+    Client *alt_tab_client;
 } DWNState;
 
 extern DWNState *dwn;

include/workspace.h

@@ -50,6 +50,10 @@ void workspace_focus_next(void);
 void workspace_focus_prev(void);
 void workspace_focus_master(void);
 
+void workspace_alt_tab_next(void);
+void workspace_alt_tab_prev(void);
+void workspace_end_alt_tab(void);
+
 void workspace_mru_push(int workspace, Client *client);
 void workspace_mru_remove(int workspace, Client *client);
 Client *workspace_mru_get_previous(int workspace, Client *current);