This is now done by the config endpoint module

and drop the WpBaseEndpoint controls entirely

This keeps track of the default endpoint and selects a default
based on endpoint priorities when devices are discovered

Clear self->pending_endpoint before sending the done signal,
because the signal will trigger a new endpoint to be added in the
unit test and this may happen before g_clear_object is called,
in which case adding the new endpoint fails

to avoid name clashing with the upcoming WpEndpoint interface
that is going to be the common interface of Wp{Proxy,Exported}Endpoint

This avoids hearing mono audio only on the left speaker

the _can_link function was previously assuming that the target
stream is always specified in the configuration file

The role defined in the endpoint-link configuration files must have higher
priority than the one set in the endpoint. If none of them are set, the config
policy fallbacks to the lowest one defined in the streams configuration file

This will be replaced by a new policy based on configuration files

This was causing a memory corruption and crash because the
simple-endpoint-link was not calling finalize of the endpoint-link
and the GWeakRefs pointing to the endpoints were not uninitialized,
causing g_object_unref later to try to write to them (on free'ed memory)

* rework how global objects are stored in the core
* rework how users get notified about global objects
  and proxies of remote global objects

The purpose of this change is to have a class that can manage
objects that are registered in the core or signalled through the
registry. This object can declare interest on certain types
of global objects and only keep & signal those objects that it is
interested in. Additionally, it can prepare proxy features and
asynchronously deliver an 'objects-changed' signal, which is
basically telling us that the list of objects has changed.

This is useful to simplify port proxies management in WpAudioStream.
Now the stream object can declare that it is interested in ports
that have "node.id" == X and the object manager will only maintain
a list of those. Additionally, it will emit the 'objects-changed'
signal when the list of ports is complete, so there is no reason to
do complex operations and core syncs in the WpAudioStream class
in order to figure out when the list of ports is ready.

As a side effect, this also reduces resource management. Now we
don't construct a WpProxy for every global that pipewire reports;
we only construct proxies when there is interest in them!

Another interesting side effect is that we can now register an
object manager at any point in time and get immediately notified
about remote globals that already exist. i.e. when you register
an object manager that is interested in nodes, it will be immediately
notified about all the existing nodes in the graph. This is useful
to avoid race conditions between connecting the signal and objects
beting created in pipewire

This is no longer used and it is the wrong approach anyway.
A mixer GUI needs to list all endpoints and figure out the controls
from the streams on its own, using the new endpoints API.