Move pa_format_info_to_sample_spec_fake() to core-format

I will need to use the function from outside libpulse.

I added the channel map argument, because the function will be called
from another function that is expected to initialize the channel map.
I don't know if it's in practice necessary, but it shouldn't do any
harm either.

src/pulsecore/core-format.h

@@ -0,0 +1,31 @@
+#ifndef foocoreformathfoo
+#define foocoreformathfoo
+
+/***
+  This file is part of PulseAudio.
+
+  PulseAudio 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.
+
+  PulseAudio 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 Lesser General Public License
+  along with PulseAudio; if not, write to the Free Software
+  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
+  USA.
+***/
+
+#include <pulse/format.h>
+
+/* For compressed formats. Converts the format info into a sample spec and a
+ * channel map that an ALSA device can use as its configuration parameters when
+ * playing back the compressed data. That is, the returned sample spec doesn't
+ * describe the audio content, but the device parameters. */
+int pa_format_info_to_sample_spec_fake(pa_format_info *f, pa_sample_spec *ss, pa_channel_map *map);
+
+#endif