keyvaults admin generation failure

[qiaozha]

see https://dev.azure.com/azure-sdk/internal/_build/results?buildId=4468503&view=logs&j=47092895-c7c8-567a-c7a6-8c88f3ec178e&t=d293a8e8-c6af-5091-cdf7-4c66482dd6f2

[MaryGao]

This issue RangeError: Maximum call stack size exceeded happened with below self-referenced union case, and this issue happened both in RLC and Modular.

union Error {
  null,
  {
    /**
     * The error code.
     */
    @visibility("read")
    code?: string,

    /**
     * The error message.
     */
    @visibility("read")
    message?: string,

    /**
     * The key vault server error.
     */
    @visibility("read")
    @encodedName("application/json", "innererror")
    innerError?: Error,
  },
}

[qiaozha]

pending Azure/typespec-azure#2088 for modular fix.