type:code doesn't work in smartSearchField

Created by: rvantonder

I get no results when I do type:code. code isn't a documented option, or supported in the backend. I think we should add it and this is a good thing to have. It's not super straightforward, because we will currently return results for both file content and file paths by default, and restricting it to just file contents isn't we allow right now (we'd have to filter things from Zoekt). So, for now, I suggest we remove type:code.