Make AstalWp.Device give the `form-factor`

[PartyWumpus]

Is your feature request related to a problem? Please describe.
Often device.icon gives me too little control over what the icons look like (I have no idea what the full set of icons a device can ask for is, so it's easy for an icon i don't have to show up). My solution to this in AGS v1 was just to fallback using the form_factor instead.

Describe the solution you'd like
It would be nice if a AstalWp.Device contained form factor info

Describe alternatives you've considered
I could just live with it and have a single fallback icon (<icon icon={Icon.lookup_icon(d.icon) ? d.icon : "audio-x-generic"}/>) instead of using the form factor to more accurately guess.

Additional context
I have no idea where form factor actually comes from. It's possible it isn't a wireplumber thing, in which case feel free to completely disregard this issue, but I'm strugging to find any docs which list all the valid wireplumber device properties.

[kotontrion]

The initial goal of the AstalWp lib was to roughly achieve feature parity with ags v1 audio service and i left it at that, as other libs needed more attention.

I started to implement some more missing features and adding access to more properties like this one will be part of that.