`NoAccessLevelOnExtensionDeclaration` doesn't apply access modifier on members guarded by `#if`

Reproducer:

```swift
public extension Foo {
#if os(ios)
    static let x = 10
#endif
    static let y = 10
}
```

Gets formatted to

```swift
extension Foo {
  #if os(ios)
    static let x = 10
  #endif
  public static let y = 10
}
```

But should be

```
extension Foo {
  #if os(ios)
    public static let x = 10
  #endif
  public static let y = 10
}
```

rdar://146604297