add computed property name support for template inputs

### Clear and concise description of the problem

Would like to be able to set the name for a property through template input, repo [here](https://typespec.io/playground?c=bW9kZWwgSW5wdXRUZW1wbGF0ZTxUTmFtZSBleHRlbmRzIHN0cmluZywgVD4gewogIMUdOiBUOwp9CgrLPiBpc89HIk15xCwiLCB7fT47Cg%3D%3D&e=%40typespec%2Fopenapi3&options=%7B%7D)

### 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.