This is to provide easy access to default nodes from the scripts

Do not use WpState at all when use-persistent-storage=FALSE; keep all
the configured default nodes in memory and forget them upon restart

* default endpoints no longer make sense
* follow upstream logic of configured vs effective default nodes
* store node names in json inside the metadata, as upstream does
* add default video source

It looks nicer to have groups of features in 'Features.'
instead of 'Feature.'

It is not needed as si-standard-link can be configured with port contexts

Makes it easier when handling session items in Lua

The get_endpoint_acquisition() vmethod has also been moved to WpSiPortInfo, and
therefore renamed to get_acquisition().

Allows checking if the endpoints are still valid before releasing the
acquisition. Sometimes the endpoints are destroyed before the link, and
releasing acquisition is not needed. There is no way to check that with raw
pointers.

Depends on pipewire!555 to avoid breaking stuff

Useful for rule matching on nodes where the rules are also matching
properties of the card.

This creates devices earlier, allowing the use of per-device
codec configuration via the standard rules

See pipewire/pipewire!509

Because it is only meant to be used with audio nodes

Because it is only meant to be used with audio nodes

Also simplifies all tests using base-test-fixture.h

Allows using object managers to listen for registered items