No we should not support enum types derived from strings

[Andrei Alexandrescu]

On 5/12/21 6:36 AM, Jonathan M Davis wrote:
> Having isSomeString accept types that implicitly converted to string would
> be a disaster.

Sadly that's exactly what StringTypeOf does: https://run.dlang.io/is/8xqPKr

We should eliminate all uses of StringTypeOf from phobos.