There is a lightbulb tool in VS2017 to add missing cases (the IDE0010), but no sort feature.
This "add missing cases" feature follows the order of values in the enum declaration, which is what you'd usually want.
Sorting an existing switch case list in place would be an idea for an extension.
But seriously, why would you really ever need to do this?
We usually sort our enum-based switch cases in just the same order they're defined in the enum itself, and if that happens to be alphabetical, fine, otherwise their order may have a functional meaning implied by the author of the enum, and that can be replicated in the switch case order.
If the cases are still empty, you could use a VS extension like this one to sort the enum fields in the declaration, remove all cases, and execute the IDE0010 "add missing cases" tool.