AstalWp: add missing features

[kotontrion]

The AstalWp lib initially only implemented enough to achieve feature parity with the audio service of ags v1 and is missing some useful features.

Todo:

• per channel volume controls
• set an endpoints target device
• configure device routes
• give the user access to more pipewire properties
• docs

If there are feature missing in the list above, let me know.

Changes:

breaking

• the AstalWpEndpoint class was renamed to AstalWpNode. There are two new Classes: AstalWpStream and AstalWpEndpoint, both inherit from AstalWpNode.
• is-default property was moved from AstalWpNode to AstalWpEndpoint
• use glib-mkenums, which might break packages. eg in Arch it is part of glib-devel, so this needs to be added as a build dependency

non breaking

• AstalWpStream
  • target-serial: int represents the serial number of the Endpoint this stream targets.
  • target-endpoint: AstalWpEndpoint the target endpoint of this stream
  • media-role
  • `media-category``
• AstalWpEndpoint
  • device-id: uint the id of the device associated with this endpoint
  • device: AstalWpdevice same, but the device object instead of id
  • is-default: boolean was moved here from AstalWpNode
  • routes: List of AstalWpRoute objects
  • active-route-id and active-route for the currently active route
• AstalWpNode
  • state : AstalWpNodeState the current state of this node (eg, running, idle)
  • channel-volumes: GList(AstalWpChannelVolume) a list containing volume information for each channel
  • get_pw_property: gets a property of the underlying pipewire object. This allows to read properties, which are not wrapped as GObject properties yet.
• AstalWpdevice
  • form-factor: string
• AstalWpChanelVolume
  • name: string the name of the channel
  • volume: double the volume
  • volume-icon: string the volume icon
• AstalWpRoute object representing a Route
• AstalWpWp now has a ready signal, which is emitted after streams/endpoints/devices/etc are initially loaded

Note: kotontrion/wirecontrol#1 does make use of these new feature.

closes #295
closes #318

[PartyWumpus]

Hey, I was bored so I decided to see if I could implement this stuff on my own. I've got form-factor and and endpoint target device on a branch PartyWumpus/astal/wireplumber-improvements. No idea if what I've written is any use, but thought I'd share. I could make a PR but this does what you're already planning to do so I wasn't sure.

(sidenote: being able to instantly just use endpoint.device.formFactor in TS with only these quick changes is great, astal is a really cool tool)

[kotontrion]

This PR is now basically ready except for the docs and a little cleanup. Also requires a bit more testing. I did only test it using wirecontrol, linked in the original message.