[http-client-java] mgmt premium, fix sample entry point and serviceClient reference for autorest

When generating premium mgmt samples from Swagger, we switched to use individual entry points in https://github.com/microsoft/typespec/pull/9845. However, for multi-service scenario(appservice, resources, etc)
1. entry point now be the aggregated Manager, instead of the individual packages, e.g. There's no `PolicyManager`, but rather `ResourceManager`.
2. service client got separate too, instead of residing inside of the entry Manager. e.g. There's no `ResourceManager.serviceClient().getPolicyDefinitions()`, but rather `ResourceManager.policyClient().getPolicyDefinitions()`.