Fix streaming type types when they are required

[AllanZhengYP]

• Fix a bug when streaming member shape is required:
  before:

export type UploadDocumentsCommandInput = Omit<UploadDocumentsRequest,"documents"> & {
  documents?: UploadDocumentsRequest["documents"] | string | Uint8Array | Buffer;
};

now:

export type UploadDocumentsCommandInput = Omit<UploadDocumentsRequest,"documents"> & {
  documents: UploadDocumentsRequest["documents"] | string | Uint8Array | Buffer;
};

• Because command input and output shape is now possibly different to the ones exported from models/index.ts. So now SDK client uses the ones exported from commands to compose input/output type union, instead of those exported from models/index.ts. Although in most cases they should be the same types

Codegen: aws/aws-sdk-js-v3@ee37569

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