A base class for objects that can have optional
features enabled and disabled. The intention is to make
this the superclass of WpProxy.

Instead of following the augment() pattern of WpProxy,
this one follows the more advanced transition pattern
that has been previously implemented in WpSessionItem.

The Dbus device reservation has been moved into a separate module, and has also
been refactored to allow reserving a device name before an actual device is
created. Devices now are created and destroyed by the monitor depending on
whether PipeWire owns the device or not. This also simplifies a lot the device
activation module to always enable devices when they are created, and never
worry about checking whether a device is acquired by PipeWire or not.

Allows implementing device specific endpoint creation logic, which is currently
needed for bluetooth endpoints as they need to be created differenly.

Apparently git cannot directly clone at an arbitrary commit,
it must be a branch or a tag

because otherwise the metadata unit test fails

* Implement the proxy properly with info caching, methods, etc
* Get rid of useless variables and includes

meson.build:
When the 'wrap_mode' option is set to 'nodownload' use a system version
of cpptoml. This does not require using git and having a network
connection during build, which is important for Linux packaging
infrastructure.

subprojects/cpptoml.wrap:
Pin revision to last release tag (v0.1.1).

lib/wptoml/*.cpp:
Remove 'include/' prefix from all cpptoml related includes, at is not
required.

Closes #17

Related to #18

* add library.name to not require adding `add-spa-lib` in pipewire.conf
  or wireplumber.conf for this to work
* add a commented local=true; it can be useful to run those nodes
  locally for testing, sometimes

there are underlying issues with the state management of the graph,
so it's not a very good idea to rely on it to activate / deactivate
our convert node depending on the links that exist

instead, track the links ourselves and create/destroy the corresponding
links to the target node accordingly; it's a more robust approach

it was also not entirely correct that we would previously configure
the convert node to be a driver (node.driver=true); maybe this caused
the underlying issues in the first place... we don't need it now
anyway, so it's gone

Just like media-session does
JACK nodes should be left untouched

1. device export proxies must be destroyed manually since they are
   not associated with the WpRegistry
2. the monitors should not disconnect before all WpSpaDevice objects
   are destroyed; remove the manual disconnect call and let GObject
   ref counting do its job (the core will disconnect when its last ref
   count is dropped after the last monitor plugin is destroyed)

* do not copy the full alsa node properties set
* use a node description that makes the nodes look better in JACK
* use . instead of / as a separator for the node.name, like elsewhere
* add audio.convert spa lib association in the tests that use si-convert;
  previously it used to work because library.name was present in the
  properties copied from the adapter (and it so happens that the adapter
  lives in the audioconvert spa plugin as well ...)

JACK uses : as a separator to distinguish the port name
from the node name, so it ends up doing wrong separations
if we have : in the node name