Move `SdkBody` and `bytestream` into `aws-smithy-types` (#3026)

## Motivation and Context
Takes care of the first part of
https://github.com/awslabs/smithy-rs/issues/3053 (the remaining part is
denoted as `TODO(runtimeCratesVersioningCleanup)` and until that and
https://github.com/awslabs/smithy-rs/issues/3033 are done the issue will
not be closed).

## Description
This PR moves from `aws-smithy-http` to `aws-smithy-types`:
- the `SdkBody` struct
- the `byte_stream` module

Within the origin crate, we leave "breadcrumbs" (i.e. reexports) for
existing customers of the items above so they are not broken by the
move.

We have just moved `SdkBody` to `aws-smithy-types` without renaming it
to see how it looks there. However, as
[TODO(naming)](https://github.com/awslabs/smithy-rs/pull/3026/files#diff-090c503b779024fdadb8ac97465c80438635df82e62c42b0d85b588a303d9a95R28

)
says, we can choose to rename it to just `Body`. Curious to hear what
the reviewers think.

## Testing
Relied on the tests in CI.

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Co-authored-by: Russell Cohen <rcoh@amazon.com>