Return impl AsyncBufRead from into_async_read

[utkarshgupta137]

Motivation and Context

The tokio StreamReader implements AsyncBufRead, but we're returning AsyncRead currently. If a user needs an AsyncBufRead, then they've to wrap the returned value in tokio BufReader for no reason. Since ByteStream doesn't implement Stream anymore, one has to either wrap the returned value unnecessarily or write a wrapper similar to this function.
See #2983 (comment).

Description

Simply changed the return type to say impl AsyncBufRead. Since AsyncBufRead is a super-set of AsyncRead, this is not a breaking change.

Testing

The code example tests it.

Checklist

• I have updated CHANGELOG.next.toml if I made changes to the AWS SDK, generated SDK code, or SDK runtime crates

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[jdisanti]

Thanks for fixing this! ❤️

[jdisanti]

It looks like the changes to the example aren't compiling:

 error[E0599]: no method named `lines` found for opaque type `impl tokio::io::async_buf_read::AsyncBufRead` in the current scope
   --> src\byte_stream.rs:434:50
    |
7   | let mut lines =  my_bytestream.into_async_read().lines();
    |                                                  ^^^^^ method not found in `impl AsyncBufRead`
    |
   ::: C:\Users\runneradmin\.cargo\registry\src\index.crates.io-6f17d22bba15001f\tokio-1.33.0\src\io\util\async_buf_read_ext.rs:342:12
    |
342 |         fn lines(self) -> Lines<Self>
    |            ----- the method is available for `impl tokio::io::async_buf_read::AsyncBufRead` here
    |
    = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
    |
2   + use tokio::io::util::async_buf_read_ext::AsyncBufReadExt;
    |

error: aborting due to previous error

[utkarshgupta137]

It looks like the changes to the example aren't compiling:

 error[E0599]: no method named `lines` found for opaque type `impl tokio::io::async_buf_read::AsyncBufRead` in the current scope
   --> src\byte_stream.rs:434:50
    |
7   | let mut lines =  my_bytestream.into_async_read().lines();
    |                                                  ^^^^^ method not found in `impl AsyncBufRead`
    |
   ::: C:\Users\runneradmin\.cargo\registry\src\index.crates.io-6f17d22bba15001f\tokio-1.33.0\src\io\util\async_buf_read_ext.rs:342:12
    |
342 |         fn lines(self) -> Lines<Self>
    |            ----- the method is available for `impl tokio::io::async_buf_read::AsyncBufRead` here
    |
    = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
    |
2   + use tokio::io::util::async_buf_read_ext::AsyncBufReadExt;
    |

error: aborting due to previous error

Fixed.

[rcoh]

I fixed external types, CI should pass now I think