We currently decide at build time whether to include screencast
support, based on whether the required gst/pipewire library headers
are installed.
That check is imprecise, because having the library headers available
at build time doesn't necessarily mean that the libraries are there
at runtime, or that the corresponding typelibs are installed.
It makes more sense to check the requirements at runtime, so prepare
for that by installing the screencast service unconditionally, but
bail out early if the dependencies aren't met.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2297>
Move the screencasting into a separate D-Bus service process, using
PipeWire instead of Clutter API. The service is implemented in
Javascript using the dbusService.js helper, and implements the same API
as was done by screencast.js and the corresponding C code.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1372
