- pw_core_info has data that represent the remote core
- pw_core properties are the properties of its pw_client,
initially inherited from the pw_context, which can be updated either
when calling pw_context_connect() or later at runtime (the pw_core
calls pw_client_update_properties() on its pw_client)

wp_core_update_properties() is made in such a way so that we can do:
```
clone = wp_core_clone(core);
wp_core_update_properties(clone, ...);
wp_core_connect(clone);
```
and get clone to have different properties than the original core,
while they still share the same pw_context underneath

also delay the "connected" signal until info is there

a method to take the internal pw_properties without copying

and do not allow writing to wrapped pw_properties,
since they are const now

the spa object undereath doesn't do that and we lose a bunch of
properties otherwise

By mistake, WpImplNode was developed by keeping in mind that the proxy
returned by pw_core_export() is a PW_TYPE_INTERFACE_Node, but this
is not true. It's actually a ClientNode...

Unfortunately, making WpImplNode work as if it was a WpNode is
not so easy, especially when it comes to handling params, which
need to be queried syncrhonously on the underlying spa_node.

So, instead of fixing WpImplNode to work as a WpNode, we choose to
disconnect them. This way, WpImplNode will not be used as a proxy
in the registry and the registry will normally create WpNode proxies
instead, making round-trips through the server to change node params.

This is necessary to finish augmenting nodes that advertise
PropInfo & Props in their param info but they don't actually have
any properties, so there is no param event emitted
(ex. the jack device nodes)

Because the sync is synchronous with the calls over the protocol,
the callback is ensured to be called after all the param events
have been emitted

otherwise we get stuck waiting for the param event
and we get warnings on the debug log

this allows the created nodes to be able to set their "device.id"
property correctly

they are not useful anymore because we hijack priv->info from the
impl subclass, so that it points to the impl info struct,
and therefore the base implementations work just fine

This reverts commit 917a019b.

so that we can filter proxies by id on object managers

- make it a GObject so that it can emit its own signals
and so that it can be shared between multiple proxies
- share the WpProps instance between endpoints, endpoint-streams
and their underlying nodes
- introduce the concept of the caching mode that redirects _set
to _set_param of the proxy that actually has the props; this allows
shared WpProps to actually set changes on the correct proxy
in a transparent way
- change methods to consume the ref of the pod and reflect that
also on wp_proxy_set_prop()
- refactor the export process on endpoints & endpoint-streams
so that they always get all the required features (info, props, bound)
and make it async so that we can take time to prepare the underlying
node to have FEATURE_PROPS
- update the props & endpoint unit tests, bringing back all the
checks that the endpoint unit test used to have