Deserialization: separate error and body deserializations

[jeremymeng]

Not blocking, not high pri but should be nice to have.

For example,

export async function _submitBatchDeserialize(result: PathUncheckedResponse): Promise<{
  body: FileContents | { contents: FileContents; contentType?: string; filename?: string };
}> {
  const expectedStatuses = ["202"];
  if (!expectedStatuses.includes(result.status)) {
    const error = createRestError(result);
    error.details = errorXmlDeserializer(result.body);
    error.details = { ...(error.details as any), errorCode: result.headers["x-ms-error-code"] };
    const restErrorCodeValue = result.headers["x-ms-error-code"];
    if (restErrorCodeValue !== undefined) {
      error.code = restErrorCodeValue;
    }
    throw error;
  }

  return _submitBatchRequestDeserializer(result.body) as any;
}

It would be great to have the error-checking part before the last return as a helper function that can be called separately without doing anything to the result.body.

In Storage we had to manually call _submitBatchSend(), _submitBatchDeserializeHeaders(), and checking for error. calling _submitBatchDeserialize() is fine because we can discard the return value. But it's doing unnecessary work. Also for other/future operations, it may not be good to consume the body.

[MaryGao]

@jeremymeng considering this is not blocking, i tentivately put it as p1 task and let me know if this is a blocking for example blocking us to do any customization. We could adjust it then.