Enable event stream operations with RPC bound protocols in client SDKs (#4036)

## Motivation and Context
Addresses aws-sdk-rust#213 and aws-sdk-rust#1188.

## Description
This PR consolidates the changes from the previous sub-PRs:
- https://github.com/smithy-lang/smithy-rs/pull/4004
- https://github.com/smithy-lang/smithy-rs/pull/4015
- https://github.com/smithy-lang/smithy-rs/pull/4023

Together, this PR enables event stream operations with RPC bound
protocols, including `SubscribeToShard` in Kinesis and `StartLiveTail`
in CloudWatchLogs in the Rust SDK.

## Testing
(consolidated bullets from the previous sub-PRs)
- Added a service integration test for cloudwatchlogs
- Added client SDK codegen tests in
`ClientEventStreamUnmarshallerGeneratorTest` to reverify
initial-response message handling
- Added client SDK codegen tests in
`ClientEventStreamMarshallerGeneratorTest` to verify initial-request
message handling
- Added `DisableStalledStreamProtectionTest`
- Confirmed a successful run in the release pipeline 

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] For changes to the smithy-rs codegen or runtime crates, I have
created a changelog entry Markdown file in the `.changelog` directory,
specifying "client," "server," or both in the `applies_to` key.
- [x] For changes to the AWS SDK, generated SDK code, or SDK runtime
crates, I have created a changelog entry Markdown file in the
`.changelog` directory, specifying "aws-sdk-rust" in the `applies_to`
key.

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