This also brings the advantage that all tools, examples, modules, components
can also be compiled standalone out-of-tree using libpipewire from the system
When the resource does add_listener, send a message to the proxy
to trigger an emission of properties.
Block the client until all properties have been notified, track
this with a ping event to the implementation.
The proxy API is the one that we would like to expose for applications
and the other API is used internally when implementing modules or
factories.
The current pw_core object is really a context for all objects so
name it that way. It also makes it possible to rename pw_core_proxy
to pw_proxy later.
Metadata allows apps to attach properties to objects that can be
read by other apps.
Not complete yet, properties should be removed when the object is
removed.
