A code refactoring to deinterpol a string

Suggested by @T-Gro

Basically it could fix the following cases:
```fsharp
let x = $"test"

let y = $"{x}"
```

Interpolation is useless here - it decreases readability and in the second case has small perf penalty. Change the code to:
```fsharp
let x = "test"

let y = x
```

Note, $"test" compiles to the "test" so it might be not worth running a code ref in the background for this case.