C# get first day of week
- C# get first day of week from date
- C# get first day of week from week number
- C# get first day of current week
- C# datetime get first day of week
- C# get first and last day of week
- C# get first and last day of current week
- C# set first day of week
- C# get first day of calendar week
- C# first day of week number
- C# get first day of next week