Function getStartOfDay

getStartOfDay(date?: Date): undefined | Date
Returns the start day date of the given date
Parameters
- Optionaldate: Date
  the date to inspect
Returns undefined | Date
the start day date of the given date
Author
David Hsing
Example
```
getStartOfDay(new Date(2023, 8, 30, 12, 12, 12));    // Date(2023, 8, 30, 0, 0, 0)
```