Cleanups: fix deprecated g_type_class_add_private()

- use G_DECLARE_ and G_DEFINE_ macros
- move all data into ClassNamePrivate
- use _get_instance_private()

This should not introduce any functional changes or breakage.

Skipped two classes (EekKeyboard and EekboardContextService) for now in
order not to break the build.

These two classes are used in some very funky WIP code that tries to
circumvent encapsulation.

(Funky code is in eekboard/key-emitter.c and eekboard/eekboard-context-service.c)

eek/eek-keysym.h

@@ -38,27 +38,7 @@ G_BEGIN_DECLS
 #define EEK_INVALID_KEYSYM (0)
 
 #define EEK_TYPE_KEYSYM (eek_keysym_get_type())
-#define EEK_KEYSYM(obj) (G_TYPE_CHECK_INSTANCE_CAST ((obj), EEK_TYPE_KEYSYM, EekKeysym))
-#define EEK_KEYSYM_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST ((klass), EEK_TYPE_KEYSYM, EekKeysymClass))
-#define EEK_IS_KEYSYM(obj) (G_TYPE_CHECK_INSTANCE_TYPE ((obj), EEK_TYPE_KEYSYM))
-#define EEK_IS_KEYSYM_CLASS(klass) (G_TYPE_CHECK_CLASS_TYPE ((klass), EEK_TYPE_KEYSYM))
-#define EEK_KEYSYM_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS ((obj), EEK_TYPE_KEYSYM, EekKeysymClass))
-
-typedef struct _EekKeysymClass EekKeysymClass;
-typedef struct _EekKeysymPrivate EekKeysymPrivate;
-
-/**
- * EekKeysym:
- *
- * The #EekKeysym structure contains only private data and should only
- * be accessed using the provided API.
- */
-struct _EekKeysym {
-    /*< private >*/
-    EekSymbol parent;
-
-    EekKeysymPrivate *priv;
-};
+G_DECLARE_DERIVABLE_TYPE (EekKeysym, eek_keysym, EEK, KEYSYM, EekSymbol)
 
 struct _EekKeysymClass {
     /*< private >*/