screenshot: Move HAVE_RECORDER check into screencast service

screenshot: Move HAVE_RECORDER check into screencast service

Some gstreamer plugins require a connection to the display server,
so if we end up initializing gstreamer before we are ourselves
fully initialized, we may end up with a locked compositor.

Avoid this by moving the runtime recorder check into the screencast
D-Bus service, so that all gstreamer calls happen out of process.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/5710

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2519>