Adds support for .NET 6.0 preview.
Features
- Updated the Microsoft .NET 5.0 assemblies for the .NET 5.0.3 runtime and made internal changes to support the .NET 6.0 preview release.
- Changed how FTP and HTTP server events are processed while the server is in the process of stopping or restarting. Client sessions will no longer be forcibly terminated while handling a request, however additional events will not be raised while the server is in its shutdown process.
- The MIME components and library will now decode encoded text in a message part when it is designated as an attachment. Previous versions would not decode text in a file attachment and would always return the encoded data. This only affects text content and binary file attachments should be stored using the ExtractFile method or MimeExtractFile function.