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 38 seconds
Status Job ID Name Coverage
  Container Prep
passed #432109
container_prep

00:00:34

 
  Build
failed #432110
build-native-meson

00:01:04

 
Name Stage Failure
failed
build-native-meson Build
  RemovedInSphinx30Warning)
/root/.local/lib/python3.7/site-packages/sphinx_rtd_theme/search.html:20: RemovedInSphinx30Warning: To modify script_files in the theme is deprecated. Please insert a <script> tag directly in your theme instead.
{{ super() }}
ninja: build stopped: cannot make progress due to previous errors.
Uploading artifacts...
build-*/meson-logs: found 2 matching files
prefix-*: found 54 matching files

Uploading artifacts to coordinator... ok
id=432110 responseStatus=201 Created token=gkUjgb7x
ERROR: Job failed: exit code 1