Remove required_ from meta.required_provider and preserve backward compatibility

We need to remove the required_ prefix from the meta.required_provider key in policies. The new key should be meta.provider. Also, we must ensure backward compatibility so that existing policies using meta.required_provider continue to function correctly.

• Update the core, specifically the function start_policy_evaluation_from_dict to handle the above case
• Write tests to ensure that policies with required_provider, and provider, both work.