Fix issue with $localDatetime using UTC.

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Fixes WebTools AZDo issue 2187534

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@shyamnamboodiripad @bleaphar

[jonsequitur]

Can you provide a test to pin the expected behavior?

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Sure it looks like we already have some that were added in a previous PR, but didn’t use the full time likely due to not being able to get an accurate asset time, so we were hiding this bug.

I’ll update the test to at least consider the hour in the format string that should reduce the likelihood of random failures as opposed to using a full datetime.

https://github.com/dotnet/interactive/pull/3505/files

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Can you provide a test to pin the expected behavior?

Added two new tests which just verify that we are using the correct timezone, added comment in tests to explain slightly different usage then other unit tests - in other tests we pass in a delegate which replaces the default product behavior so that we can match the actual time in the assertions. For this test, we don't call that overload so that we get the actual product behavior and the real GetDateTimeOffset method is called which returns either Now or UtcNow depending on the isLocal argument.