Fix S3 presigning in the orchestrator (#2738)

## Motivation and Context
This PR fixes S3 presigning in the client orchestrator implementation. A
Polly presigning fix will come in a separate PR.

This PR also:
- Renames `ClientProtocolGenerator` to `OperationGenerator` to better
represent what its generating.
- Moves `OperationCustomization` into `codegen-client` since it is
client specific and unused by the server codegen.
- Deletes the `ProtocolGenerator` base class in `codegen-core` since it
wasn't adding any value.
- Adds the concept of stop points to the orchestrator so that
orchestration can be halted before transmitting a request.
- Adds `DisableInvocationIdInterceptor`,
`DisableRequestInfoInterceptor`, `DisableUserAgentInterceptor`, and
`HeaderSerializationSettings` config bag configs to facilitate
presigning requirements.
- Fixes compilation of all S3 and Polly tests when in orchestrator mode.

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._