30% optimization of `DateTime.GetDate()`/`.Year/.Month/.Day/.DayOfYear` by 'Euclidean...

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