Add DateOnly support.

[CollinAlpert]

This PR adds support for setting cells through a DateOnly value.

[CollinAlpert]

It seems the build is failing because it uses .NET 5. .NET 5 is end-of-life and not supported anymore. Will it be possible to upgrade to .NET 6, the LTS release?

[tonyqus]

I've fixed the build issue. Sorry, I'm too lazy to get it fixed.

[CollinAlpert]

Build looks good. How does the PR itself look?

[tonyqus]

Since you changed the ICell interface, please change XSSFCell and SXSSFCell as well. They both implements ICell interface.

I'm curious why there is no compilation error if XSSFCell and SXSSFCell doesn't have SetCellValue(DateOnly value) method. Maybe a bug of .NET 6? I'm not sure

[CollinAlpert]

I was also surprised to see the build didn't fail. I assume it is because the project is built using .NET Standard and due to the preprocessor directives, the method gets hidden. I added the methods in the other implementations as well now.

[CollinAlpert]

How does it look? Can we merge this?

[tonyqus]

LGTM