The proxy takes more roundtrips to get updated and this makes the
policy fail to find a default endpoint at startup, right after
the devices have been discovered

This also removes the weak ref on the session, since the object
manager internally maintains a reference on the objects that
it manages.

to make it more usable and compatible with g_idle_add

This is useful to be able to call export() from a module init
function, which is called before the core is connected

These are set by the server on the global properties set

heavily based on the WpSession implementation

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

Otherwise, if the object manager is destroyed while a sync is in progress,
we get an invalid 'self' pointer on the callback later, which is being
called regardless

There is a bit more work that should be done in the core to avoid leaking
this ref in case pipewire disconnects before the sync is completed

The purpose of this change is to have a generic API that allows modules to read
configuration data from files under a specific directory. Since we can have many
types of configuration files, this new class maps file extensions with generic
parsers defined in the modules, giving modules full freedom to parse any kind of
data.

in finalize() the pw_proxy is already gone and we always print null

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 lifts the limitation of having a single entity externally
that augments the proxy and allows us to implement better
management of the proxies with the upcoming WpObjectManager