The 'installed' signal can be used to know that there are no
known objects that are being prepared internally, so the object
manager is ready to use.
This also improves internal state management so that the 'objects-changed'
signal cannot be fired earlier than it should. Previously there
were corner cases with complex proxy features, as the object manager
relied on the fact that after a core 'sync' it is safe to assume
that all proxies are augmented... that's not always the case.
This allows having constraints on the pw properties and the GObject
properties of the proxy, instead of just on the global properties.
This is only useful for constraints on impl proxies, since the globals
coming from the registry don't have a proxy object associated at the
time they are added in the object managers
When a new global is created, it is not certain
if the registry global event or the proxy bound event will
be fired first. In order to make sure we associate all
proxies to their WpGlobals correctly, we now wait a core sync
before exposing globals to the object managers, so that in case
the implementation proxy receives the bound event after the
registry creates the WpGlobal, we can make sure to use this
proxy instead of constructing a new one through the object managers
There are 3 kinds of WpProxy objects:
* the ones that are created as a result of binding a global
from the registry
* the ones that are created as a result of calling into a remote
factory (wp_node_new_from_factory, etc...)
* the ones that are a local implementation of an object
(WpImplNode, etc...) and are exported
Previously the object manager was only able to track the first kind.
With these changes we can now also have globals associated with
WpProxies that were created earlier (and caused the creation of the global).
This saves some resources and reduces round-trips (in case client
code wants to change properties of an object that is locally
implemented, it shouldn't need to do a round-trip through the server)
+ use the pw_proxy API to find the bound id instead
of relying on WpGlobal
This has the advantage that it works also for exported
objects and for objects that have been created by calling
into a remote factory (such as the link-factory), so we can
now know the global id of all proxies, not only the ones
that have been created by the registry.
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
