Construct this new class from both the src and sink to be able to share code
Consolidate the previous mess of open/close/start/stop into a single pair
of open/close functions in the new stream class
Since meson 0.59.0, a feature object has an `allowed()`
method which returns true when the feature is set to
'enabled' or 'auto'.
Utilize that instead of the previously used
not feature.disabled()
Make all sources in the same process with the same fd share the
connection to the server. This makes it possible to set the same
fd on multiple sources/sinks and have them all use the same
connection, like when capturing multiple monitors from screencast
with the portal.
Fixes#241
