Support the new BCL `DateOnly` and `TimeOnly` structs

[roji]

New DateOnly and TimeOnly structs are being introduced to .NET 6 as alternatives to DateTime (dotnet/runtime#49036).

[bgrainger]

As a parameter value, DateOnly could map to DATE, and TimeOnly to TIME.

When reading (e.g., with GetFieldValue<T>?) need to decide if extra data (e.g., GetFieldValue<DateOnly> on a DATETIME column, or GetFieldValue<TimeOnly> on a TIME column that is > 24 hrs) is just truncated/silently dropped, or causes an exception.

[mattjohnsonpint]

Please note that the final names for these types are DateOnly and TimeOnly and that they are now merged into the main branch for the next version of .NET 6 (preview 4 likely). Please rename the title of this issue accordingly. Thanks.

[bgrainger]

The commit written for this doesn't add support for converting from MySqlDateTime. That struct mostly exists for backwards compatibility with MySQL Connector/NET. Converting from it to DateOnly has a simple workaround: DateOnly.FromDateTime(mySqlDateTime.GetDateTime()).

[Germs2004]

Thank you for this great project. I added a vote and wanted to point out that implementing this Issue would support the project's homepage that says it's "cutting edge" and the tutorial that says it already supports DateOnly.

A connection string option to opt in is good for backwards compatibility, though the other opinion is that anyone who wants to intentionally mismatch a DATE field to a DateTime variable should be the ones who have to opt out via a connection string option.

[bgrainger]

@Germs2004 This was implemented in MySqlConnector 2.0.0.