Instead of a VST3-style polling function to test if a plugin supports a
certain layout, the plugin now explicitly enumerates the supported
layouts. This aligns better with non-VST3 plugin formats.
I've been putting this off for a while, but now is finally the day. We
already did this for CLAP a while back. This is both simpler and less
error prone.
This is needed to enable sending and receiving SysEx #54. Because
associated type defaults still are not stable, this requires every
plugin that doesn't need this to set this to the unit type:
```rust
type SysExMessage = ();
```
This will make it possible to run background tasks in a type safe way.
Sadly, this does mean that every plugin now needs to define the type
alias and constructor function since Rust does not yet support defaults
for associated types.
Only a couple of these functions would be needed during initialization.
In the next couple commits ProcessContext will get a way to access
auxiliary IO, so this really had to be separated.
This is a breaking change requiring a small change to plugin
implementations.
The reason why `Pin<&dyn Params>` was used was more as a hint to
indicate that the object must last for the plugin's lifetime, but `Pin`
doesn't enforce that. It also makes the APIs a lot more awkward.
Requiring the use of `Arc` fixes the following problems:
- When storing the params object in the wrapper, the `ParamPtr`s are
guaranteed to be stable.
- This makes it possible to access the `Params` object without acquiring
a lock on the plugin, this is very important for implementing
plugin-side preset management.
- It enforces immutability on the `Params` object.
- And of course the API is much nicer without a bunch of unsafe code to
work around Pin's limitations.
You'll likely want to add some scaling yourself anyways, so this would
just be a wasted operation since the scaling also depends on your window
function.
