ReadonlyDate: Readonly<Omit<Date,
| "setDate"
| "setFullYear"
| "setHours"
| "setMilliseconds"
| "setMinutes"
| "setMonth"
| "setSeconds"
| "setTime"
| "setUTCDate"
| "setUTCFullYear"
| "setUTCHours"
| "setUTCMilliseconds"
| "setUTCMinutes"
| "setUTCMonth"
| "setUTCSeconds">>
A Date type with mutation functions omitted.