This is an asynchronous operation class, like GTask,
but it is made to execute several operations underneath,
using a state machine, instead of just a single operation.

and in case it's missing, also #define some things to make compilation work,
since this is only available in a pipewire branch right now

This will solve a possible race condition in the unit test when destroying the
autotestsrc proxy while its node_event_info is being called.

the global is stored internally and the returned ref is only useful
in the WpProxy code, not in the registry_global() event

it doesn't matter, because we don't use it, but for the sake of readability

some code is expecting things to happen in that order...

... in case the global is removed from the registry before
the initial augment completes

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