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 4 minutes and 5 seconds
Status Job ID Name Coverage
  Container Prep
passed #293629
container_prep

00:03:01

 
  Build
failed #293630
build-native-meson

00:01:04

 
Name Stage Failure
failed
build-native-meson Build

libweston/meson.build:144:2: ERROR: Problem encountered: logind support requires dbus-1 >= 1.6 which was not found. Or, you can use '-Dlauncher-logind=false'

A full log can be found at /builds/mol/weston/build-weston-c13379c6d690fa137bd9f6735186ef7e31c5a3de-293630/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=293630 responseStatus=201 Created token=vb9wnsSq
ERROR: Job failed: exit code 1