GPU: Add debug groups

Debug groups makes it easier to view from where an error comes from.

The backend can also implement its own callback to make it easier to
follow the API call structure in frame debuggers.

source/blender/gpu/GPU_debug.h

@@ -0,0 +1,38 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2020 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup gpu
+ *
+ * Helpers for GPU / drawing debugging.
+ */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void GPU_debug_group_begin(const char *name);
+void GPU_debug_group_end(void);
+void GPU_debug_get_groups_names(int name_buf_len, char *r_name_buf);
+
+#ifdef __cplusplus
+}
+#endif