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