The new RecordVirtual API creates a virtual monitor, i.e. a region of
the stage that isn't backed by real monitor hardware. It's intended to
be used by e.g. network screens on active sessions, virtual remote
desktop screens when running headless, and scenarios like that.
A major difference between the current Record* API's is that
RecordVirtual relies on PipeWire itself to negotiate the refresh rate
and size, as it can't rely on any existing monitor, for those details.
This also means that the virtual monitor is not created until the stream
negotiation has finished and a virtual monitor resolution has been
determined.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1698>
