formats: Export more functions needed for a clean build.
All of these functions are not actually defined in format.h
(they are defined in internal.h) and thus should really be
included only in libpulsecommon and implemented in a separate
source file.
However if that approach was taken, and these functions were
included in libpulsecommon, then they would have a link time
dependancy on libpulse (as these four functions use other
pa_format_info_* functions). As the opposite is already true
(libpulse depends on libpulsecommon), this is not possible as
it creates a circular dependancy.
Thus the only option is to just to include these four functions
in the map-file, but not actually export any public headers for
them. Of course users could use this implementation by defining
them in their own headers, but the only practical problem
with this approach is naming conflicts which is unlikely to happen.