Add support for enum members

It looks like precise code intel for enum members doesn't work at all currently. ([code](https://sourcegraph.com/github.com/sourcegraph/sourcegraph/-/blob/client/search-ui/src/input/extensions/completion.ts?L33-48))

![Screenshot showing search-based intel for enum member](https://user-images.githubusercontent.com/93103176/165649737-6f50e592-3841-4f45-808b-7ab70da3ec35.png)
