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.
Good catch! However, making the changes you suggest makes all of the cases mentioned above report errors because findSymbol never seems to return a symbol for an indexed access on an Enum (or a module for that matter it looks like). It seems like the compiler should be able to find a symbol here and that this is a bug but maybe I'm missing something and it's just not possible to make the connection from the string "y" back to the enum member on M?