Warn when mapping a TimeSpan to a SQL Server time

[ajcvickers]

By default, EF Core maps .NET TimeSpan to SQL Server time. This is a problematic mapping because time is much more constrained than TimeSpan. We have discussed this many times; for example, see
#242 (comment).

With value conversions, it might be better to map TimeSpan by default to something else, as suggested in #22633. However, this is both a breaking change and may still be problematic until #10434 is robustly implemented.

However, we could generate a warning when this mapping is used.

[FrankSzendzielarz]

I would also just add to emphasize, though it's probably unhelpful, that mapping TimeSpan to Time is the direct conceptual analogy of mapping Length to Position. In fact, Position modulo 24. I.e. the mapping is just flat out wrong, so a breaking change might be warranted.