kwin: emit window fullscreen info + refactor helper script

The helper script was also refactored to minimize the amount of callbacks added and the memory used. There's no need to keep callbacks attached for non-active windows, which happened before.

Also it should be more efficient and simpler to send info over with just a single DBus call (also if more fields were to be added).

Both the script and the helper app will send/print info only if it changed since the previous one. Otherwise we'd keep spamming fullscreen false update when navigating the desktop and so on.

include/KwinWorkaround.hpp

@@ -5,8 +5,10 @@
 namespace gsr {
     struct ActiveKwinWindow {
         std::string title = "Game";
+        bool fullscreen = false;
     };
 
     void start_kwin_helper_thread();
     std::string get_current_kwin_window_title();
+    bool get_current_kwin_window_fullscreen();
 }