Add soundness check for validating .editorconfig compliance

[jakepetroules]

https://editorconfig-checker.github.io

In Swift Build we have a check to verify there are no files without a trailing newline or files with trailing whitespaces. It would be great to generalize this to an .editorconfig verifier -- we could add a soundness check that uses the python editorconfig-checker package installed via pip to achieve this.

[FranzBusch]

Sounds good to add an editor config checker. Maybe we can include that in the format job?