Hover on parameter should display haddock comment

When hovering over a parameter in a function, I want to be able to see the haddock documentation for said parameter.

`thing_inside` has a rich comment, but I always need to manually match the parameter to the type signature and find the haddock comment.

It would be much better, if on hover on `thing_inside`, I would additionally see:
```
The FreeKiTyVars is null <=> all kind variables used in the
kind signature are bound on the left. Reason:
the last clause of Note [CUSKs: complete user-supplied kind signatures]
in GHC.Hs.Decls
```

Start by locating the language server's hover handling for function parameters and how Haddock comments are available for those symbols. The issue provides no file or test names, so trace the existing hover behavior first. Done means hovering over a parameter displays its associated Haddock documentation alongside the current information.

Written by the indexing model from the issue text.