lib: Introduce Clapper GTK integration library

An easy to use GTK integration library. Meant as a GtkVideo alternative.

While GtkVideo is more of a simple example of video playback under GTK4, this
acts as a full-fledged video player in the form of a GtkWidget that can be placed
anywhere within application.

The widget offers customization options for both top header and bottom playback
controls panels. The Clapper playback API is exposed under widget "player" property
making it easy for the programmer to set media and control playback programically.

The new library will be distributed with Clapper player. This includes public headers
and GObject Introspection support.

Licensed under LGPL-2.1-or-later.

src/lib/clapper-gtk/clapper-gtk-buffering-animation-private.h

@@ -0,0 +1,41 @@
+/* Clapper GTK Integration Library
+ * Copyright (C) 2024 Rafał Dzięgiel <rafostar.github@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the
+ * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
+ * Boston, MA 02110-1301, USA.
+ */
+
+#pragma once
+
+#include <glib.h>
+#include <glib-object.h>
+#include <gtk/gtk.h>
+
+#include "clapper-gtk-container.h"
+
+G_BEGIN_DECLS
+
+#define CLAPPER_GTK_TYPE_BUFFERING_ANIMATION (clapper_gtk_buffering_animation_get_type())
+#define CLAPPER_GTK_BUFFERING_ANIMATION_CAST(obj) ((ClapperGtkBufferingAnimation *)(obj))
+
+G_DECLARE_FINAL_TYPE (ClapperGtkBufferingAnimation, clapper_gtk_buffering_animation, CLAPPER_GTK, BUFFERING_ANIMATION, ClapperGtkContainer)
+
+G_GNUC_INTERNAL
+void clapper_gtk_buffering_animation_start (ClapperGtkBufferingAnimation *animation);
+
+G_GNUC_INTERNAL
+void clapper_gtk_buffering_animation_stop (ClapperGtkBufferingAnimation *animation);
+
+G_END_DECLS