Also add a new CodecProviders builder class similar to CodecRegistries

Justification: the CodecRegistry interface extends CodecProvider, and the driver already treats the user-provided registry only as a provider, since it always wraps the user-provided one via CodecRegistries#withUuidRepresentation. Making this change would clarify that the driver effectively treats the registry as a provider.

Alternatively, we could just document this fact in MongoClientSettings so that neither we nor our users are confused about it.