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.
This now is a single vector with all of the information in the correct
order instead of the hashmaps and a vector. This avoids deduplication,
and it especially makes manual `Params` implementations a lot more
convenient since you can't mess up with mismatching IDs between the
methods.
To accommodate exactly this, the persistent fields methods also have a
default implementation and the trait has been marked as `unsafe` since
it's the programmer's responsibility to make sure these `ParamPtr`s will
remain valid.
This may hurt performance in generic UIs a bit, but it will allow you to
programatically generate custom Params implementations for repeated
Parameters structs.
On second thought, this is much better. The resulting file size will be
much smaller because only double quotes need to be escaped. It's also
easier to read at a glance.
Sadly there's not really a safe way to do this otherwise, but if you
really want to have persistence this way and absolutely need it to be
lock-free (because you're going to use it from the GUI thread), then you
can implement your own PersistentField.
I much prefer kebab case, but snake case is better here since Rust would
convert it to snake case when used as an identifier anyways and you also
can't use snake case modules without explicit module path attributes.
