Implement IUtf8SpanFormattable on DateTime, DateTimeOffset, DateOnly, TimeOnly, TimeS...

Implement IUtf8SpanFormattable on DateTime, DateTimeOffset, DateOnly, TimeOnly, TimeSpan, Char, Rune (#84469)

* Implement IUtf8SpanFormattable on DateTime, DateTimeOffset, DateOnly, TimeOnly, TimeSpan, Char, Rune

* Address PR feedback

Also dedup Utf8Formatter for TimeSpan with TimeSpan's new IUtf8SpanFormattable implementation and a little more cleanup.

And fix parameter name of TryFormat to match approved name.