[ty] Make auto-import work in the playground
It turned out that we weren't quite funneling the new completion data
all the way through.
I followed the docs for [`CompletionItem`] for the Monaco editor. It's
similar, but not identical, to the LSP protocol specification.
[`CompletionItem`]: https://microsoft.github.io/monaco-editor/typedoc/interfaces/languages.CompletionItem.html
