Add editorconfig defaults

[ShadowCommander]

Some things in the codebase don't have defaults right now. Last I checked the defaults were basically Rider's defaults, but those aren't the same as Visual Studio's defaults, so we need to decide and actually put them in the .editorconfig.

https://github.com/space-wizards/space-station-14/blob/master/.editorconfig

Microsoft has a page for coding conventions in C#
https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/inside-a-program/coding-conventions
https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/coding-style.md

There are also a lot of commented out settings in the .editorconfig that are in the default .editorconfig but weren't set when I cleaned it up.

[ShadowCommander]

Current things I've found that don't have consistent usage in code

private const

private (property)