Make the protocol client connect call async with a callback when it
completes.
Move the connect methods into separate files, add an empty connect
method that will use the screencast portal to get a pipewire fd.
Use the remote intention to get the connect method.
Add some better error reporting.
Make a link factory and use create-object to make links. That way
we can have different kinds of links based on the factory and we
can also hide the factory when link creation should be blocked.
