6111: Add assist for converting the base of integer literals. r=SomeoneToIgnore a=vlakreeh
This PR adds an assist similar to Intellij's [convert number to](https://i.imgur.com/JH6wstP.png). It also does a small refactor to [assists/src/tests.rs](fc34403018/crates/assists/src/tests.rs) to add the ability to specify the resolved assist for a specific action within an assist group.
## Demo
![Demo of the assist in action](https://i.imgur.com/MBhdPFH.gif)
Co-authored-by: vlakreeh <zeb@zebulon.dev>