Migrate to new configuration file-based DE portals declaration

Since xdg-desktop-portal 1.18 it replaces the `UseIn` key.
The obsolete key will be temporarily kept for compatibility reasons.

Signed-off-by: Mavridis Philippe <mavridisf@gmail.com>

interfaces/CMakeLists.txt

@@ -44,6 +44,8 @@ configure_file(xdg-desktop-portal-tde.desktop.cmake
 
 install(FILES tde.portal DESTINATION ${XDG_PREFIX}/share/xdg-desktop-portal/portals)
 
+install(FILES tde-portals.conf DESTINATION ${XDG_PREFIX}/share/xdg-desktop-portal)
+
 install(FILES ${CMAKE_CURRENT_BINARY_DIR}/org.freedesktop.impl.portal.desktop.tde.service
         DESTINATION ${DBUS_SESSION_DIRECTORY})
 

interfaces/tde-portals.conf

@@ -0,0 +1,2 @@
+[preferred]
+default=tde;