Outlining: collapsing the first union case collapses all cases

There seems to be a bug in outlining for union types, where collapsing the first case collapses all cases, instead of only the first. This works properly for the second case onwards. See the repro below for an example.

**Repro steps**

```
type Test =
| A of
id:string
* name:string
| B of
id:string
* name:string
| C of
id:string
* name:string
```

1. Paste the above code into VS2019.
2. Collapse the first union case.


**Expected behavior**

Collapsing the first union case should collapse ONLY the first case.

**Actual behavior**

Collapsing the first union case collapses ALL cases.

**Known workarounds**

N/A

**Related information**
Windows 10 Enterprise (10.0.17763)
.NET Core 2.1.7021
Visual Studio 2019 (16.1.3) (but same on 2017)
Visual F# Tools 10.4 for F# 4.6 (16.1.0-beta.19253.3+42526fe359672a05fd562dc16a91a43d0fe047a7)