Audaspace: add support for PulseAudio on Linux

This adds PulseAudio as audio backend on Linux.
PulseAudio is the main audio engine used on most,
if not all, Linux distributions today.

Ref T86590

doc/doxygen/doxygen.intern.h

@@ -60,6 +60,9 @@
 /** \defgroup audopenal Audaspace OpenAL
  *  \ingroup audaspace
  */
+/** \defgroup audpulseaudio Audaspace PulseAudio
+ *  \ingroup audaspace
+ */
 /** \defgroup audpython Audaspace Python
  *  \ingroup audaspace
  */