Viewporter implementaion (#585)

Implementation of the `wp_viewporter` core protocol and some bugfixes

src/render/Renderer.hpp

@@ -40,6 +40,7 @@ public:
     bool                shouldRenderWindow(CWindow*);
     void                ensureCursorRenderingMode();
     bool                shouldRenderCursor();
+    void                calculateUVForWindowSurface(CWindow*, wlr_surface*, bool main = false);
 
     bool                m_bWindowRequestedCursorHide = false;