Provide a way to rename body parameters when using Azure.Core templates.

### Clear and concise description of the problem

There's currently no simple way to rename a body parameter when using some Azure.Core templates, such as LongRunningResourceCreateOrReplace. This means folks have to re-write their operations or change templates simply to rename a body parameter. It would be nice to have a way to do these renames while still using the same standard template.

Example of an operation that cannot rename a body parameter simply:
```
op deidentifyDocuments is DeidentifyOperations.LongRunningResourceCreateOrReplace;
```

I was hoping we could access the body with metatypes or some other method.

### 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.

Start with the LongRunningResourceCreateOrReplace template and the deidentifyDocuments operation example in the issue. Determine how body parameters are exposed for renaming without rewriting the operation or template; done means a standard Azure.Core template supports this rename directly.

Written by the indexing model from the issue text.