Unreachable code detection does not respect local scopes and throw statements

## Version Used
VS 2022 Version 17.11.5
Roslyn 4.11.0 (5649376e0e5f)

Project info
C# 12.0
.NET 8.0

## Steps to Reproduce

Use the following code:

```csharp
public static int Add(int a, int b)
{
{
return a + b;
}

throw new InvalidOperationException();

{
throw new InvalidOperationException();
}

{
const int x = 523;
throw new InvalidOperationException();
}

{
throw new InvalidOperationException();
}
}
```

## Expected Behavior

In VS, the unreachable code will dim out showing that the dimmed out region is unreachable. In the above example, we expect all the code from the throw statement onwards to be dimmed out.

## Actual Behavior

The resulting dimming is very different and limited to the scope that starts with non-throw statements.

Reproduce the behavior in Visual Studio 2022 with Roslyn 4.11.0 using the C# code in the issue. Start by tracing Roslyn's unreachable-code detection for local scopes and throw statements. Done means the editor dims all code after the first unreachable point, including subsequent scoped blocks.

Written by the indexing model from the issue text.