Fix dictionaries with enums as keys

[PerfectlyNormal]

Not too uncommon to have a

public class ResponseDto
{
    public Dictionary<State, int> Counts { get; set; }
}

which got translated to the non-functional

import { number } from '...';

export interface ResponseDto {
  counts: { [key: State]: number };
}

this handles converting enums to number, so we get

// no import needed

export interface ResponseDto {
  counts: { [key: number]: number };
}

which is more what we would expect