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 1 minute and 42 seconds (queued for 1 second)
Status Job ID Name Coverage
  Container Prep
passed #287907
container_prep

00:01:05

 
  Build
failed #287908
build-native-meson

00:00:36

 
Name Stage Failure
failed
build-native-meson Build

pipewire/meson.build:15:3: ERROR: Problem encountered: Pipewire plugin requires libpipewire-0.2 which was not found. If you rather not build this, set "pipewire=false".

A full log can be found at /builds/mol/weston/build-weston-bc76eba29ddffbe043387458af43421fe7be10c3-287908/meson-logs/meson-log.txt
Uploading artifacts...
build-*/meson-logs: found 2 matching files
prefix-*: found 54 matching files

Uploading artifacts to coordinator... ok
id=287908 responseStatus=201 Created token=nPcBegUx
ERROR: Job failed: exit code 1