[tcgc] support multiple services in one tsp specification

When the typespec define multiple services, each service contains different apiVersions, authentication and clients(see following) TCGC need to provide api to retrieve apiversions, authentications and clients belongs to one service

getVersions(service: Service): list all the api-versions of the service
listClients(service: Service): lists all the clients which belongs to the services.
getAuthentication(service: Service): return the authentications the service supported.
support service scope for @client decorator


@versioned(Versions1)
@service({
  title: "HttpbinServer",
  version: "1.0.0",
})
@server(
  "https://{domain}.{tld}",
  "Httpbin endpoint",
  {
    @doc("second-level domain, use httpbin")
    domain?: string = "httpbin",

    @doc("top-level domain, use org")
    tld?: string = "org",
  }
)
namespace Typespec.Server {
  @route("/status/{code}")
  interface ServerOp {
    status(@path code: int32): OkResponse | NoContentResponse;
  }
}
enum Versions1 {
    @useDependency(Azure.Core.Versions.v1_0_Preview_1)
    "2022-05-15-preview"
  }

enum APIVersions {
    v1: "v1",
  }

@versioned(APIVersions )
@service({
  title: "ContosoServer",
})
@server(
  "{Endpoint}/contoso/{ApiVersion}",
  "Service endpoint",
  {
    @doc("Service endpoint")
    Endpoint: string,

    @doc("Api Version")
    @path
    ApiVersion: APIVersions,
  }
)
namespace ContosoServer {

  @route("/contoso")
  interface ServerOp {
    get(@path code: int32): OkResponse | NoContentResponse;
  }
}

### Tasks
- [ ] https://github.com/Azure/typespec-azure/issues/441
- [ ] https://github.com/Azure/typespec-azure/issues/441

Azure / typespec-azure

[tcgc] support multiple services in one tsp specification #1024