Async endpoint links

See merge request gkiagia/wireplumber!15

If we have properties, strtok will return strings from there as tokens
and the error will appear later as we will attempt to parse an incomplete
GVariant. It is better to catch this early so that we can print a more
useful error message.

So now we can do:
---
load-module C foo {
  "property": <"value">
}
---

The starting brace is still required to be on the same line
as the load-module.

Properties are expected to be a GVariant a{sv} dictionary,
specified in the GVariant text format:
https://developer.gnome.org/glib/stable/gvariant-text.html

Unregister fixes

See merge request gkiagia/wireplumber!14

This is a bit of a hack, temporarily needed for AGL.

Async endpoints

See merge request gkiagia/wireplumber!13

Currently this will just grant full access to all clients.
A future version will refine that to grant access to specific
objects only.

Registry

See merge request gkiagia/wireplumber!12

Fixes #1

This is a situation that always happens on startup, so let's not
spam with warnings

signal emission apparently does not work in _finalize()

Fixes some critical warnings from remote-endpoint.c because disconnection
from the destroyed endpoints did not happen