transform inputs for platform specific type helpers

[kuhe]

there is a type helper that narrows payload types, currently only for outputs

import { S3 } from "@aws-sdk/client-s3";
import { NodeJsClient } from "@smithy/types";

const s3 = new S3({}) as NodeJsClient<S3>;

await s3.putObject({
    Bucket: '',
    Key: '',
    Body: new Blob() // helper makes this a type error, must use Node.js http(s) payload types like Buffer/Uint8Array/string
})

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

const body = get.Body; // helper narrows this to SdkStream<IncomingMessage>

this PR adds type narrowing to inputs as well.

[kuhe]

related to aws/aws-sdk-js-v3#5361