renderer: add popup fade-in-out (#11313)

Adds xdg popup fade-in and fade-out

src/render/OpenGL.hpp

@@ -298,6 +298,7 @@ class CHyprOpenGLImpl {
 
     std::map<PHLWINDOWREF, CFramebuffer>        m_windowFramebuffers;
     std::map<PHLLSREF, CFramebuffer>            m_layerFramebuffers;
+    std::map<WP<CPopup>, CFramebuffer>          m_popupFramebuffers;
     std::map<PHLMONITORREF, SMonitorRenderData> m_monitorRenderResources;
     std::map<PHLMONITORREF, CFramebuffer>       m_monitorBGFBs;