GeezerVison

With this PR we display the name 'nothing' for empty union types. Empty union types can occur when control flow type analysis concludes that there is no possible type for a variable that matches the preceding type guards in a particular code path. For example:

function foo(x: string | number) {
    if (typeof x === "string") {
        x;  // x is of type string here
    }
    else if (typeof x === "number") {
        x;  // x is of type number here
    }
    else {
        x;  // x is of type nothing here
    }
}

The 'nothing' type cannot be explicitly named, it has no members, and no other types are compatible with it.