Consider adding a linting and formatting to the repo

## Describe the proposal

There's a technique I've used before that we might want to apply here:

- Add `.editorconfig`
- Document how to use `dotnet format` at the command line
- Add a CI job like: https://github.com/dotnet/tye/blob/master/.github/workflows/format.yml

EditorConfig is fairly lightweight and flexible and can enforce as many or as few code style rules as we want. There unfortunately isn't really a *standard* set of rules accepted widely in the C#-o-verse - but it's possible to arrive at a really reasonable and minimal set.

The side benefit is that editors like VS and Rider are aware of EditorConfig and will configure their settings appropriately - so most users developing on the repo end up falling into the defaults ... ahem ... by default.