visualstudio open namespace codefix has wrong indentation in some cases

In indented context, the open namespace code fix puts the declaration at wrong indentation level.

It doesn't always affect the code, but when there are type extensions, it breaks it.

```fsharp
module Foo =
open System

type DateTime with
member x.X() = ()

let a () =
let t = Task.Factory.StartNew(fun () -> 1) // use the code fix on Task
()
```


**Related information**

VS2019 16.8