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

[XiaofeiCao]

When generating premium mgmt samples from Swagger, we switched to use individual entry points in #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().

[XiaofeiCao]

This currently only applies to resources (when generating using multiple tsp compile). Multi-service has no issue, since it has only one entry point.