Function isSheetDate

isSheetDate(v): v is SheetDate
True for a SheetDate.
Parameters
- v: unknown
  any value
Returns v is SheetDate
true for a sheet date
Example
```
isSheetDate(new SheetDate(1));   // true
```
Since
1.1.99
- Defined in src/lib/table/sheet/sheet-values.ts:41