Issue Description:

When enum is defined like:

enum AccountType {
  case savings, checking
}

and code that uses it:

let account: AccountType
switch account { }

we could provide cursor refactoring, which whenever the cursor is anywhere on switch keyword lets a user to expand missing switch cases to the form:

let account: AccountType
switch account {
    case .savings: <#code#>
    case .account: <#code#>
}

This works just like current Expand default but is more convenient to use when user doesn't have default case written yet.