This code is based on the similar implementation for JACK.

This allows for transparent JACK and PulseAudio emulation. With this you
can essentially replace your entire audio framework with just PipeWire
for almost no configuration.

Co-authored-by: Jan Tojnar <jtojnar@gmail.com>

This adds two tests. One is for whether the paths used by the module are
present, while the other is for testing functionality of PipeWire
itself. This is done with the recent addition of installed tests by
upstream.

This splits PulseAudio and JACK emulation into separate outputs. Doing
so provides a number of benefits.

First it fixes pw-pulse and pw-jack. Prior to this they pointed to bogus
locations because the environment variables were not evaluated.
Technically fixing this only requires setting libpulse-path and
libjack-path to any absolute path not necessarily separate outputs but
it comes as a nice result.

Secondly it allows overriding libpulseaudio with pipewire.pulse in many
packages. This is possible because the new outputs have a more standard
layout.

Since PulseAudio is required as a build input, the libraries mistakenly
reference the original libpulse.so rather than the custom one.

As of PipeWire 0.3.8, the library is bundled with a slightly modified
version of PulseAudio's udev rules.

Without this it is possible for PipeWire to fail in binding the dbus socket.

While both strings and lists are valid, lists are the more accurate type
and only they can properly merge with each other.

This replaces the temporary RPATH fix with the new upstream patch  from
jtojnar. It also removes the reference to the dev output.