Support for self in #[async_ffi]

[yavko]

This is pretty self explanatory, would be nice to be able to use it with functions that use self
EDIT: This is kinda needed as all abi_stable methods in traits have to use self

[oxalica]

In which case do you need to make a method instead of a standalone function returning FfiFuture?
I expect it's only used right on the FFI boundary. See https://docs.rs/async-ffi/0.4.1/async_ffi/#performance-and-cost

[yavko]

In which case do you need to make a method instead of a standalone function returning FfiFuture? I expect it's only used right on the FFI boundary. See docs.rs/async-ffi/0.4.1/async_ffi/#performance-and-cost

I'm creating a plugin system, and would like for it to be standardized and have support for Async, and Sync methods, even if Async comes with a cost, its not really a big deal for me.