plugin: Add GL memory importer

Add "clapperglimporter" and a base class for creating GL importers. This module allows importing GL memory into GdkTexture.

lib/gst/plugin/importers/gstclapperglimporter.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2022 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 Library General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 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
+ * Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library 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 "gstclapperglbaseimporter.h"
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_CLAPPER_GL_IMPORTER (gst_clapper_gl_importer_get_type())
+G_DECLARE_FINAL_TYPE (GstClapperGLImporter, gst_clapper_gl_importer, GST, CLAPPER_GL_IMPORTER, GstClapperGLBaseImporter)
+
+#define GST_CLAPPER_GL_IMPORTER_CAST(obj)        ((GstClapperGLImporter *)(obj))
+
+struct _GstClapperGLImporter
+{
+  GstClapperGLBaseImporter parent;
+};
+
+G_END_DECLS