This is needed to support Ardour. These extra hops and serialization
steps will probably hurt performance, but outside of some huge hacks (to
connect the components directly anyways) there's not much else we can
do.
This has much fewer moving parts, and it's probably more understandable.
There was also a race condition in the previous implementation, so
there's that.
This requires a super hacky workaround because the UI thread can be
currently blocked by the plugin calling `IPlugFrame::resizeView()` from
the Win32 message loop.
This way every relevant object instance will get its own thread for
handling these calls. The alternative would be creating a full fat
Vst3MessageHandler pair for all object instances, but that would be a
huge waste.
This is quite a huge refactor, but note everything is consistent (and
we're going to need one or two more of these `Vst3*Proxy` objects).
Right now nothing extends `IHostApplication`, but this way it will be
trivial to add support for more host context interfaces.
We're also going to need this for `IEditController`. Separating all of
these classes will also keep everything much more maintainable with all
of these associated structs.
Directly serializing and deserializing into objects was and more
boilerplate heavy (since we now need two implementations even though we
only use one), and also much less flexible because we can't wrap
payloads in structs or provide optional values that way.
Robbert van der Helm