Translate DateTimeOffset.ToUnixTime[Seconds|Milliseconds]

[ascott18]

ToUnixTime* methods on DateTimeOffset can be translated in SQL Server as DATEDIFF(second|millisecond, '1970-01-01T00:00:00.000', [Date]).

This can even be done today verbosely with EF.Functions as EF.Functions.DateDiffSecond(DateTimeOffset.UnixEpoch, date). It would be nice if translation of ToUnixTimeSeconds/ToUnixTimeMilliseconds was supported natively.

[Marusyk]

Please assign it to me

[ajcvickers]

@Marusyk Feel free to submit a PR. Note that EF7 is closed for new features, so the PR should target the main branch and we will not merge it until after EF7 is closed down.