This makes the API much, much nicer (especially consuming the egui
wrapper), and it also avoids having to lock the plugin instance which is
obviously very bad if the plugin is also supposed to be processing audio
on another thread.
This needs a lot of work. We need widgets that know how to deal with our
parameters, and also basic widgets for things like meters. Egui-baseview
also has a couple quirks left. Most notably it only updates when
actively moving over the GUI (which means VU meters look pretty janky)
and it randomly panics.
