type parameters in tooltip can be bogus / inconsistent with whole signature when 'a is used for an explicit type parameter

In Visual Studio, with the following function, hovering on the `b` parameter shows `'a` as parameter type, which is incorrect (`b` isn't of same type as parameter `a`) and inconsistent with what is shown hovering on the function itself.

```fsharp
let a (a: 'a) b (c:'b) = a,b,c
```


note also that it won't honor `c` parameter type when hovering on the `z` function and show the wrong one for `b`, whenever `'a0` is used explicitly (this is a corner case and less of an issue, revealing an implementation detail).

```fsharp
let z (a: 'a0) b (c:'a) = a,b,c
```