fix(types): fix client type transforms

[kuhe]

aws/aws-sdk-js-v3#4720

This PR fixes typechecking for aggregated client usage in the optional type transforms from changes to the Command shapes using Command.classBuilder.

preview of the integration test I'll add to AWS SDK:

import { GetObjectCommand, S3, S3Client } from "@aws-sdk/client-s3";
import type { AssertiveClient, BrowserClient, NodeJsClient, UncheckedClient } from "@smithy/types";

{
  // default, no validation for undefined values
  const s3 = new S3({});

  await s3.listBuckets();
  await s3.listBuckets({});

  // @ts-expect-error (missing Bucket)
  s3.getObject({
    Key: undefined,
  });

  s3.getObject({
    // @ts-expect-error (unrecognized field)
    UnknownProperty: undefined,
  });

  const get = await s3.getObject({
    Bucket: undefined,
    Key: undefined,
  });

  // @ts-expect-error (Body may be undefined)
  await get.Body.transformToString();

  await get.Body?.transformToString();
  await get.Body!.transformToString();
}

{
  // the assertive client requires that inputs/outputs are of the right type
  // excluding '| undefined'.
  const s3_assertive = new S3() as AssertiveClient<S3>;
  const s3Client_assertive = new S3Client() as AssertiveClient<S3Client>;

  await s3_assertive.listBuckets();
  await s3_assertive.listBuckets({});

  s3_assertive.getObject({
    Bucket: "undefined",
    // @ts-expect-error (undefined not assignable to string)
    Key: undefined,
  });
  s3Client_assertive.send(
    new GetObjectCommand({
      Bucket: "undefined",
      // type transform is unable to validate within Command ctor.
      Key: undefined,
    })
  );

  // @ts-expect-error (missing Key)
  s3_assertive.getObject({
    Bucket: "undefined",
  });

  {
    const get = await s3_assertive.getObject({
      Bucket: "undefined",
      Key: "undefined",
    });

    // @ts-expect-error (Body is optional)
    await get.Body.transformToString();

    await get.Body?.transformToString();
    await get.Body!.transformToString();
  }

  {
    const get = await s3Client_assertive.send(
      new GetObjectCommand({
        Bucket: "undefined",
        Key: "undefined",
      })
    );

    // @ts-expect-error (Body is optional)
    await get.Body.transformToString();

    await get.Body?.transformToString();
    await get.Body!.transformToString();
  }
}

{
  // unchecked client also removes the possibility
  // of optionality '?' in addition to '| undefined'.
  const s3_unchecked = new S3({}) as UncheckedClient<S3>;
  const s3Client_unchecked = new S3Client() as UncheckedClient<S3Client>;

  await s3_unchecked.listBuckets();
  await s3_unchecked.listBuckets({});

  s3_unchecked.getObject({
    Bucket: "undefined",
    // @ts-expect-error (undefined not assignable to string)
    Key: undefined,
  });
  s3_unchecked.send(
    new GetObjectCommand({
      Bucket: "undefined",
      // type transform is unable to validate within Command ctor.
      Key: undefined,
    })
  );

  // @ts-expect-error (missing Key)
  s3_unchecked.getObject({
    Bucket: "undefined",
  });

  {
    const get = await s3_unchecked.getObject({
      Bucket: "undefined",
      Key: "undefined",
    });

    await get.Body.transformToString();
  }

  {
    const get = await s3Client_unchecked.send(
      new GetObjectCommand({
        Bucket: "undefined",
        Key: "undefined",
      })
    );

    await get.Body.transformToString();
  }
}

{
  // platform specific clients.
  const s3_browser = new S3({}) as BrowserClient<S3>;
  const s3Client_browser = new S3Client() as BrowserClient<S3Client>;
  const s3_node = new S3() as NodeJsClient<S3>;
  const s3Client_node = new S3() as NodeJsClient<S3>;

  {
    const get = await s3Client_browser.send(
      new GetObjectCommand({
        Bucket: "undefined",
        Key: "undefined",
      })
    );
    get.Body!.tee();
  }
  {
    const get = await s3_browser.getObject({ Bucket: "undefined", Key: "undefined" });
    get.Body!.tee();
  }

  {
    const get = await s3Client_node.send(
      new GetObjectCommand({
        Bucket: "undefined",
        Key: "undefined",
      })
    );
    get.Body!.pause();
  }
  {
    const get = await s3_node.getObject({ Bucket: "undefined", Key: "undefined" });
    get.Body!.pause();
  }
}