wayland: refactor: remove ‘struct config’ pointer from wayland struct

The global config doesn’t necessarily reflect the correct
configuration to use - we should *always* use the current terminal
instance’s conf pointer.

* Move selection override modifier mask to the key_binding_set struct
* Always warn if XDG activation is unavailable, not just if
  bell.urgent is set (we no longer have access to this information)
* Pass ‘bool presentation_timings’ as a parameter to wayl_init()
* Remove ‘presentation_timings’ member from the ‘terminal’ struct

Closes #932

terminal.h

@@ -591,7 +591,6 @@ struct terminal {
 
         size_t search_glyph_offset;
 
-        bool presentation_timings;
         struct timespec input_time;
     } render;