Intellisense broken in VisualFSharp solution in VS

Please provide a succinct description of the issue.

**Repro steps**

Provide the steps required to reproduce the problem:

1. Open VisualFSharp solution in VS
2. Go to any file in FSharp.Editor project (always seems to happen there but usually also other projects)

**Expected behavior**

We semantic coloring, type hints, tooltips, F12 works, etc.

**Actual behavior**

None of that works

**Known workarounds**

Edit all .fsproj files (e.g. add a whitespace character anywhere).

touch-projects.fsx
(Thanks copilot!)

```fsharp
open System
open System.IO

let addWhitespaceToFsprojFiles (directory: string) =
let fsprojFiles = Directory.GetFiles(directory, "*.fsproj", SearchOption.AllDirectories)
for file in fsprojFiles do
let content = File.ReadAllText(file)
printfn "Modifying %s..." file
File.WriteAllText(file, content + " ")

printfn "Enter the directory to crawl:"
let directoryToCrawl = Console.ReadLine()
addWhitespaceToFsprojFiles(directoryToCrawl)
```

**Related information**

VS 17.12 p2, but likely also other versions.