30% optimization of `DateTime.GetDate()`/`.Year/.Month/.Day/.DayOfYear` by 'Euclidean affine functions' (#72712)
* Optimize DateTime.GetDate()/.GetDatePart() by 'Euclidean affine functions'
* Code style
* Refactoring: avoid switch and 'var' keyword; add March1BasedDayOfNewYear constant
* Fix build
* Add [MethodImpl(MethodImplOptions.AggressiveInlining)] to GetDatePart()
* revert relevant comments from original code
* Inline calculations into properties: Year, Month, Day, DayOfYear instead of Common GetDatePart() function
* Fix indentation
* align comment