SwiftPM should include a default .editorconfig for new packages

[timsneath]

Description

With Xcode now respecting .editorconfig files (see image below), we should include a default editor config file when SwiftPM creates a new package (e.g. with swift package init). This would give VSCode useful context on how to support Swift files and reduce inconsistency when transitioning between Xcode and VSCode for a single project.

@Jeehut has proposed a simple basic template here:
https://gist.github.com/Jeehut/e5b7559da355a1f243d9c012fe63edc4

Thanks for the suggestion, @Jeehut!