Constant folding in computed enum members

Now const enums can only be used in property access\index access so after erasure the leave nothing in the code. However let's say allow them to be merged with value modules. 
```
const enum E {A}
module E {var x = 1}

var y = E; // now such usage of E will be prohibited but if E is merged with value module it should be legal
var z = y.A; // in runtime this code will fail  
```
Handling such cases will definitely make code more complicated and don't think it is worth it