Clean up spread logic for responses

### Clear and concise description of the problem

We have made the [decision to clean up the spread logic for parameter inputs](https://github.com/Azure/typespec-azure/issues/1043). However, the response logic is still messy. We're putting response on the backburner because there is no active confusion among spec authors, it is just leading to more convoluted-than-necessary emitter logic. We will wait until [traits is redesigned](https://github.com/microsoft/typespec/issues/1619).

The current thinking is modifying templates to add `@bodyRoot` (code [here](https://github.com/Azure/typespec-azure/pull/1037)).

### Checklist

- [X] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [X] Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [X] Read the [docs](https://azure.github.io/typespec-azure/).
- [X] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.