It can be a bit tricky because the "installed" signal may be fired
from inside the context of wp_core_install_object_manager(),
in which case the main loop should not be executed (or it will never quit)

We can now call wp_proxy_request_destroy() on endpoint links and
the WpImplEndpointLink together with the session item that created
it will be cleaned up

+ better logs by default
+ allow loading modules in tests

+ enable the new log writer on the executables
+ enable structured logging in the tests

* core no longer exposes create_remote/local_object
* node, device & link have constructor methods
  to enable the create_remote_object functionality
* added WpImplNode to wrap pw_impl_node and allow creating
  "local" node instances
* added WpSpaDevice to wrap spa_device and allow creating
  "local" device instances
* exporting objects in all cases now happens by requesting
  FEATURE_BOUND from the proxy, eliminating the need for WpExported
* replaced WpMonitor by new, simpler code directly in module-monitor
* the proxy type lookup table in WpProxy is gone, we now
  use a field on the class structure of every WpProxy subclass
  and iterate through all the class structures instead; this is
  more flexible and extensible