Release v0.10.0

This was accidentally left in as a result of my testing
from #459

Fixes #449.

With the v0.9.0 release of UniFFI, non-threadsafe interfaces are explicitly
deprecated. This commit removes support for non-threadsafe interfaces entirely,
making threadsafety the default and only supported mode. In practice, for
any `interface` declared in the UDL:

* Its implementation must be `Sync` and `Send`.
* Its methods cannot accept a mutable `&self` parameter.

The `[Threadsafe]` attribute may still be specified explicitly in the UDL
file, but will result in a deprecation warning and is otherwise ignored.

We don't have a good way to write tests for the following, but I've manually
verified that:

* A non-`Send+Sync` interface implementation produces a compile-time error.
* Use of the `[Threadsafe]` attribute results in a deprecation warning.

Co-authored-by: Neil P. <npars@users.noreply.github.com>
Co-authored-by: Mark Hammond <mhammond@skippinet.com.au>

Combined with [ADR-0004](https://github.com/mozilla/uniffi-rs/blob/main/docs/adr/0004-only-threadsafe-interfaces.md
) this is the last significant decision to be made on the path to
allowing us to [pass around object instances](#419).

In the previous implementation, a concurrent method call and call
to `destroy()` could result in the Rust code trying to access a
freed handle in the handlemap. This is caught cleanly by the handlemap,
but only as a last resort; it should never be allowed to happen in
practice.

This commit changes the way destruction works on the Kotlin objects
to use a reference count, avoiding freeing the underlying Rust object
until all method calls using it have completed.

Fixes #457.