hrtfapo: Add CreateHrtfApo() stub.

dlls/hrtfapo/Makefile.in

 MODULE = hrtfapo.dll
+
+C_SRCS = \
+	main.c

dlls/hrtfapo/hrtfapo.spec

-@ stub CreateHrtfApo
+@ stdcall CreateHrtfApo(ptr ptr)
 @ stub CreateHrtfApoWithDatasetType
 @ stub CreateHrtfEngineFactory
 @ stub IsHrtfApoAvailable

dlls/hrtfapo/main.c

+/*
+ * Copyright (C) 2023 Mohamad Al-Jaf
+ *
+ * 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
+ */
+
+#include "hrtfapoapi.h"
+
+#include "wine/debug.h"
+
+WINE_DEFAULT_DEBUG_CHANNEL(xaudio2);
+
+HRESULT WINAPI CreateHrtfApo(const HrtfApoInit *init, IXAPO **xapo)
+{
+    FIXME("(%p, %p): stub!\n", init, xapo);
+    return E_NOTIMPL;
+}