Test and iterate on TS expandable hover apis

To try it:

- Build this TS branch and set it as your workspace TS version: https://github.com/microsoft/TypeScript/pull/59940
- In VS Code `"typescript.experimental.expandableHover": true`

Let's test out TS's current implementation of expandable hovers. The main question is if the UI is good enough as-is, or if it turns out we need something different, which may require API changes