Function fromDayOfWeek

fromDayOfWeek(dayName: string, locale?: string): null | number
Converts a day name to its corresponding number in the specified locale. Performs a case-insensitive comparison with both long and short day names. Returns the day number using 0-based indexing (0 = Sunday, 6 = Saturday).
Parameters
- dayName: string
  The name of the day to convert (e.g., "Sunday", "Sun", "Dimanche")
- locale: string = 'en-US'
  The locale to use for parsing (default: 'en-US')
Returns null | number
The day number (0-6) or null if not found
Example
```
// Returns 1
fromDayOfWeek('Monday')
```
Example
```
// Returns 1
fromDayOfWeek('Lundi', 'fr-FR')
```
Example
```
// Returns 2
fromDayOfWeek('Di', 'de-DE')
```
- Defined in datetime.ts:135