Rework DateTime struct

- Add DebuggerBrowsableState attributes to hide several fields from debugger.
- Add UTC and ticks mask to properly handle tick values following .NET implementation.
- Correct handling of ticksAtOrigin on most code location where it was being used.
- Replace individual calls to get date time parts with a single call passing a parameter with the requested part.
- Correct several documentation comments with the correct origin and final years supported by nF.
- Replace code with expression body on several properties.
- Correct use of internal field _ticks by using the public property.
- Add DebuggerDisplay attribute and respective formating property to be able to display DateTime objects correctly in VS debugger.

Signed-off-by: josesimoes <jose.simoes@eclo.solutions>