[WIP] Breaking changes in dotnet-format 6.x

- We are moving into the .NET 6 SDK (See https://github.com/dotnet/format/issues/1268). There will be no need to install dotnet-format as a global tool or local tool.
- As part of the move into the .NET SDK, we have changed our command line options. (see https://docs.microsoft.com/en-us/dotnet/core/tools/dotnet-format)
- Organize imports was moved from being a whitespace formatter to running as a code style formatter.
- CodeStyle and 3rd Party Analyzers will only run if they are specifically configured in your .editorconfig.
- Default severity for CodeStyle and 3rd Party Analysis is now `warning`.
- We now use the highest version .NET 6 SDK that is installed rather than trying to match the global.json configuration.