input: better cursor image infrastructure

Improves handling of cursor images/surfaces
Fixes an issue with decos and cursors
Fixes #3471

src/Window.hpp

@@ -339,6 +339,7 @@ class CWindow {
     wlr_box                  getFullWindowBoundingBox();
     SWindowDecorationExtents getFullWindowExtents();
     wlr_box                  getWindowInputBox();
+    wlr_box                  getWindowMainSurfaceBox();
     wlr_box                  getWindowIdealBoundingBoxIgnoreReserved();
     void                     updateWindowDecos();
     pid_t                    getPID();