Error on updating file with interface+class with event parameter that's inside class

Tried updating BouncerService.cs:
```csharp
public interface IBouncerService {
event Action Bounced;
// ..
}

public class BouncerService : IBouncerService {
public struct Case { /* .. */ }
public event Action Bounced = delegate { };
// ..
}
```
Got following SourceCodeCombined.cs:
```csharp
public interface IBouncerService__Patched_{
event Action Bounced;
// ..
}

public class BouncerService__Patched_: IBouncerService {
public struct Case { /* .. */ }
public event Action Bounced = delegate { };
// ..
}
```
With following error:
```
error CS0738: 'BouncerService__Patched_' does not implement interface member 'IBouncerService.Bounced'. 'BouncerService__Patched_.Bounced' cannot implement 'IBouncerService.Bounced' because it does not have the matching return type of 'Action'.
```

Start with the BouncerService.cs example and inspect the generated SourceCodeCombined.cs output, focusing on how the interface and class are renamed. Reproduce the compiler error and trace the hot-reload transformation that produces the renamed types. Done means the transformed example compiles without CS0738 and the event still matches the interface member.

索引モデルが issue の本文から書いたものです。