Description of the change

Renames javy emit-provider to javy emit-plugin. This is a breaking change of Javy's command line interface.

Why am I making this change?

Part of #768. This will keep the terminology consistent in Javy.

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli and javy-plugin do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.