Features are flags, therefore we must NEVER use them without a shift,
otherwise bad mistakes happen, like the previous mistake of declaring
WP_SESSION_FEATURE_LINKS as the number after WP_SESSION_FEATURE_ENDPOINTS,
which ended up being (WP_SESSION_FEATURE_ENDPOINTS | WP_PROXY_FEATURE_PW_PROXY)
and it was always becoming available together with the ENDPOINTS feature.
* 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
