Add Support For MultiService Clients with No Client Decorator

[jorgerangel-msft]

There is a new azure spector scenario for this https://github.com/Azure/typespec-azure/blob/main/packages/azure-http-specs/specs/service/multiple-services/main.tsp. The support for this should go in MTG.

[jorgerangel-msft]

The generated surface API should follow https://gist.github.com/jorgerangel-msft/22a2c91d15a299917c9079fd92e870ef#alternative-independent-top-level-clients