Xext: geext: unexport GERegisterExtension() and document it

Not used by any external module (eg drivers), so no need to keep it
exported. Also documenting it.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

Xext/geext_priv.h

@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: MIT OR X11
+ *
+ * Copyright © 2024 Enrico Weigelt, metux IT consult <info@metux.net>
+ */
+#ifndef _XORG_GEEXT_PRIV_H
+
+#include <X11/Xproto.h>
+
+typedef void (*XorgGESwapProcPtr) (xGenericEvent *from, xGenericEvent *to);
+
+/*
+ * Register generic event extension dispatch handler
+ *
+ * @param extension base opcode
+ * @param event swap handler function
+ */
+void GERegisterExtension(int extension, XorgGESwapProcPtr swap_handler);
+
+#endif /* _XORG_GEEXT_PRIV_H */