Add formatting via .editorconfig

[LucDeCaf]

Adds a default .editorconfig file using dotnet new editorconfig and runs dotnet format.

The config makes the following somewhat opinionated choices with the goal of maximising consistency:

• Tab size of 4
• Insert newlines at EOF
• Ordered imports
• Allman curly braces
• Space before and after inheritance colon (class Cow : Animal, not class Cow: Animal or class Cow:Animal)

Most of the options are the default options created by dotnet new editorconfig, except for the following:

• insert_final_newline: false to true