[Proposal] 'switch all' enhancement for enums

When switching on enums, I would like to get a compile time error if I missed a case. Simple usage would be:

```
enum EnumValues { First, Second, Third }

EnumValues myEnumValue;

switch all (myEnumValue)
{
  case First:
  case Second:
   <--- compile time error if default statement is missing or any other enum value
}
```

All is obviously optional and only works for enums.
