Add pipewire plugin

It is quite similar to the remoting plugin. It just exports the frames via
pipewire instead of the builtin GStreamer pipeline.
It implements the same virtual output API. Virtual outputs can be created
by adding 'pipewire-output' sections to weston.ini.

The generated frames can be accessed with any pipewire client. e.g. with
GStreamer:

gst-launch-1.0 pipewiresrc ! video/x-raw,format=BGRx ! ...

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
2 jobs for pipewire in 3 minutes and 55 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Container Prep
passed #306739
container_prep

00:03:00

 
  Build
passed #306740
build-native-meson

00:00:54