intellisense XML documentation does not display F# function parameters

Hover documentation on functions displays the XML summary but misses out any parameter descriptions from xml comments:

```
/// description of mypara
```

#### Repro steps

Provide the steps required to reproduce the problem

1. Create a new .NET Core console app F# project in VS 2017 15.8.2 from the create new dialog

2. Add code in program.fs as below:

```
open System

/// tets function with three parameters
///
/// silly
/// sillier
/// silliest
let testFunc a b c = a+b+c

[]
let main argv =
printfn "Hello World from F#!"
0 // return an integer exit code
```

3. hover mouse over testFunc

#### Expected behavior

Hover appears with summary and parameter descriptions for a,b,c.

#### Actual behavior

Hover appears with summary but no parameter descriptions

#### Known workarounds

None

#### Related information

Provide any related information

* Operating system: w10
* Branch
* .NET Runtime, CoreCLR or Mono Version: .NET Framework 4.7.03056

* Editing Tools (e.g. Visual Studio Version): 2017, v15.8.2
* Indications of severity: Minor, but very annoying.