Macro ffi_support::implement_into_ffi_by_pointer

macro_rules! implement_into_ffi_by_pointer {
    ($($T:ty),* $(,)*) => { ... };
}

Implements [IntoFfi] for the provided types (more than one may be passed in) by allocating $T on the heap as an opaque pointer.

This is typically going to be used from the "Rust component", and not the "FFI component" (see the top level crate documentation for more information), however you will still need to implement a destructor in the FFI component using define_box_destructor!.

In general, is only safe to do for send types (even this is dodgy, but it's often necessary to keep the locking on the other side of the FFI, so Sync is too harsh), so we enforce this in this macro. (You're still free to implement this manually, if this restriction is too harsh for your use case and you're certain you know what you're doing).