[5.11] Zoned date time fixes

[thelonelyvulpes]

Fixes for ZonedDateTime.

• Introduce Ambiguous bool property, Creating ZonedDateTime with out a datetime kind, or using a datetime kind local with a named Zone:Zone.of(string), meant we could create an ambiguous date time.
• Introduce ZonedDateTime.AmbiguityReason enum flags type.
• Introduce Reason AmbiguityReason property for ZonedDateTimes, to allow users to see why a value is considered ambiguous.
• Introduce UtcSeconds long property which is the understood monotonic timestamp from unix epoch in UTC.
• Fix ZonedDateTime lazily parsing when returned from a query, now it is parsed immediately.
• Fix ZonedDateTime not supporting values outside of range of BCL Date Types
• Add Ticks Property, and constructor which can be used for easy interop with nodatime's Instant