backend, virtual_keyboard: set the time_nsec field of relevant events

Backends modified: libinput (with microsecond precision), X11 (with
millisecond precision), RDP (with millisecond precision), and Wayland
(with nanosecond precision if the host server supports the
input-timestamps protocol, otherwise millisecond precision); and
virtual-keyboard protocol (with millisecond precision).

types/wlr_virtual_keyboard_v1.c

@@ -85,6 +85,7 @@ static void virtual_keyboard_key(struct wl_client *client,
 	}
 	struct wlr_event_keyboard_key event = {
 		.time_msec = time,
+		.time_nsec = time * 1000000,
 		.keycode = key,
 		.update_state = false,
 		.state = state,