Make Ariakit Composite API standard

[andrewhayward]

Reakit is now gone (#53278) and Composite is implemented entirely with Ariakit. However, Ariakit's API is only exported as a private V2, and the public (albeit __unstable) export is a legacy implementation designed to maintain Reakit's API.

We need to monitor usage, and decide when to...

• ...export and stabilize the new version of the component Composite: stabilize new ariakit implementation #63564
• ...move all consumers away from the private API export and remove the private API export Composite: stabilize APIs #63569
• ...deprecate the __unstable legacy implementation Composite: deprecate legacy, unstable version #63572

✍️ Dev Note

• see this dev note) for the unstable component's refactor
• see the dev note in Composite: stabilize APIs #63569 for the stabilization of the new Composite component

[ciampo]

Closing as the new implementation of Composite is now exported as a stable API, while the previous unstable version is marked as deprecated.