[TCGC] Regression of perf optimization

[tadelesh]

In this PR: TCGC changed the way of finding the orphan model. However, this PR did not change the getGeneratedName logic which also contain the logic of find the orphan model. This cause regressions:

1. Report error of @azure-tools/typespec-client-generator-core/duplicate-client-name Client name: "" is duplicated in language scope

union Verbosity {
  "low" | "medium" | "high",
  null,
}

union ReasoningEffort {
  "none" | "minimal" | "low" | "medium" | "high" | "xhigh",
  null,
}

@@usage(ReasoningEffort, Usage.input);

@@usage(Verbosity, Usage.input);

2. Naming change from EouDetection to EouDetection1

@service
@versioned(Versions)
namespace VoiceLive;

enum Versions {
  v1,
}

@discriminator("model")
@usage(Usage.input)
model EouDetection {
  `model`:
    | "semantic_detection_v1"
    | "semantic_detection_v1_en"
    | "semantic_detection_v1_multilingual"
    | string;
}

@usage(Usage.input)
model AzureSemanticDetection extends EouDetection {
  `model`: "semantic_detection_v1";

  @minValue(0)
  timeout_ms?: int32;
}