Fix for issue #858 (disallow incrementing/decrementing the value of enum)

Fix for issue #858. Updated the baselines associated with incrementing and decrementing enum types as well.  

This fix is a pretty simple but would it make more sense to add a new SyntaxKind for EnumAccess? I haven't looked too deeply into this but I just wonder if there are other places where we have to check IndexAccess and PropertyAccess to see if they really are accessing an Enum that a refactor like this would simplify.
Yes, I agree that sounds like a bug. IndexedAccess should act like PropertyAccess if the index is a string literal that denotes a member the compiler knows about.