Date and time types use UTC instead of the user's time zone

[rpetrusha]

Date and time types use UTC instead of the user's time zone

Related to #92, #149, dotnet/docs#10296

Consider the following code:

Console.WriteLine($"It is now {DateTime.Now} local time.");
Console.WriteLine($"It is now {DateTime.UtcNow} UTC.");
Console.WriteLine($"Your time zone is {TimeZoneInfo.Local.DisplayName}.");

When run interactively, it produces the following output:

It is now 03/12/2019 16:11:47 local time.
It is now 03/12/2019 16:11:47 UTC.
Your time zone is UTC.

When run on my local system, it produces the following output:

It is now 3/12/2019 9:11:37 AM local time.
It is now 3/12/2019 4:11:37 PM UTC.
Your time zone is (UTC-08:00) Pacific Time (US & Canada).

UTC appears to be used by default as the user's local time zone rather, and the UTC offset available from the user's browser is not used.