leverage new completion features to provide hover on (some) unsaved code

[zth]

This leverages the new unsaved completion code to get hovers on some unsaved code.

I would eventually like this to also work on assigned identifiers, like (all unsaved):

let fff = makeSomeRecord()
//   ^hov should show `someRecord`, but it doesn't because it doesn't handle the actual assigned identifier
let ccc = fff
//               ^hov here it works though

But this is a win nonetheless so adding support for something like that can be a separate thing.

[cristianoc]

Nit: there's a bit of redundancy.
allFiles comes from package.
There are functions that take both allFiles and package (or full). So they' don't really need all those args.
I guess allFiles can be either a function of package, or directly a field there. So it's computed on the spot when needed instead of being passed around.

[zth]

Will fix in separate PR.

[cristianoc]

I had not noticed much the business of completionsGetTypeEnv vs completionsGetTypeEnv2. Is there ever a reason for using the former given the latter is more powerful?

[zth]

Probably not. Mostly a bridge for migrating to the new one. Will take care of this as we do our major refactor of all of this new functionality.