ipc: add an input event

This adds an ipc event related to input devices. Currently the
following changes are supported:
- added: when an input device becomes available
- removed: when an input device is no longer available
- xkb_keymap_changed: (keyboards only) the keymap changed
- xkb_layout_changed: (keyboards only) the effective layout changed

include/ipc.h

@@ -34,6 +34,7 @@ enum ipc_command_type {
 
 	// sway-specific event types
 	IPC_EVENT_BAR_STATE_UPDATE = ((1<<31) | 20),
+	IPC_EVENT_INPUT = ((1<<31) | 21),
 };
 
 #endif

include/sway/input/keyboard.h

@@ -52,6 +52,7 @@ struct sway_keyboard {
 	struct sway_seat_device *seat_device;
 
 	struct xkb_keymap *keymap;
+	xkb_layout_index_t effective_layout;
 
 	struct wl_listener keyboard_key;
 	struct wl_listener keyboard_modifiers;

include/sway/ipc-server.h

@@ -2,6 +2,7 @@
 #define _SWAY_IPC_SERVER_H
 #include <sys/socket.h>
 #include "sway/config.h"
+#include "sway/input/input-manager.h"
 #include "sway/tree/container.h"
 #include "ipc.h"
 
@@ -19,5 +20,6 @@ void ipc_event_bar_state_update(struct bar_config *bar);
 void ipc_event_mode(const char *mode, bool pango);
 void ipc_event_shutdown(const char *reason);
 void ipc_event_binding(struct sway_binding *binding);
+void ipc_event_input(const char *change, struct sway_input_device *device);
 
 #endif