Passing decorators as argument to decorators

### Clear and concise description of the problem

In cases where conditional application of decorators (e.g. versioning or some form of selector language for the target) could be useful, it would be interesting to be able to pass in one or mode decorators as arguments to other decorators.

E.g.

```
@iifVersion('<=1', @route("/v1"), @route("v2"))
op doStuff(): void;
```

(while there is a magic expression to evaluate as a string in this example, one could certainly come up with other ways to express it)

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Read the [docs](https://typespec.io/docs/).
- [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.