compositor: Generalize VT switching as a session_signal
Instead of a callback from the tty module, we now have a compositor level
signal that fires when our session is activated or deactivated.
diff --git a/src/compositor.c b/src/compositor.c
index 8c9e0fe..6206480 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -2908,6 +2908,8 @@
wl_signal_init(&ec->update_input_panel_signal);
wl_signal_init(&ec->seat_created_signal);
wl_signal_init(&ec->output_created_signal);
+ wl_signal_init(&ec->session_signal);
+ ec->session_active = 1;
ec->output_id_pool = 0;