hyprctl/layers: print pid for layershell clients (#9468)

Adds a `getPID()` fn to layershell to print it in `hyprctl layers`

src/desktop/LayerSurface.hpp

@@ -61,6 +61,8 @@ class CLayerSurface {
     std::string                szNamespace = "";
     UP<CPopup>                 popupHead;
 
+    pid_t                      getPID();
+
     void                       onDestroy();
     void                       onMap();
     void                       onUnmap();