Hover tooltips should always show inferred types

[ChrisEPhifer]

Background / Problem

In the Haskell Language Server (HLS), hovering over any term in a program displays documentation (if available) and the term's inferred type. In the case of polymorphic terms, both the most-general type and the instantiation of the type at the current term is shown. For example, the saturated type of the term optional can be seen at the bottom of the tooltip:

In RA, however, there are terms where the only type shown in tooltips is the most-general type; no instantiation of type variables:

(There is nothing but the usual "Go to..." links below the examples seen in the screenshot.)

Feature Request

It would be lovely if, like HLS, RA could display fully saturated/instantiated types for every term upon hover. This would improve users' ability to reason locally about polymorphic types used in concrete ways; this is especially helpful for deeply-nested data structures using standard library collections in complex ways (such as the application from which I collected the above screenshot.)

My apologies if I somehow managed to duplicate an issue for this feature! Thank you in advance for your thoughts and effort :)

[Veykril]

I'll close this issue in favor of #13394 as that has more details and ideas around this improvement. It's definitely something we want to look into.